First off, I think the tail tint is just a shed coming on. I wouldn't worry about that right now unless it turns pitch black or shrivels up, but again I'm pretty sure that's just a shed coming.
So her back right foot and leg did end up swelling up? And she still has the lump on her other back leg if I recall? I'm going to assume now, just like I mentioned before, that she probably has gout. I'm basing this on the swelling, the lump on her knee joint, and the fact that she is obviously in ACUTE pain. You're husbandry has always been good and her diet/calcium supplementing has always been good, so that usually rules out MBD, as does the great amount of ACUTE pain that she is acting like she's in. MBD typically will not cause them to seem like they are in pain, nor does it stop them from trying to move, they still try to move normally, they just end up walking oddly and usually flipping over onto their backs often. It does not look like MBD to me at all, nor does it look like a Vitamin B1 deficiency or any type of neurological issue. She hasn't had any tremors or twitching as far as I know either, is that correct? If not, then I'm pretty sure it's most likely the start of gout. The good news is that it's completely treatable, but she does need to get to an experienced reptile vet that has a lot of experience with bearded dragons, not an exotics vet who doesn't have experience with bearded dragons or with gout. Gout is unfortunately becoming very common is young bearded dragons, so any experienced or certified reptile specialist vet will be familiar with the signs and symptoms of gout in bearded dragons, as well as what tests need to be run to positively diagnose gout, and how to treat it successfully. So if you have to drive a few hours one way to get to an experienced reptile vet then that's what you need to do, trust me it is sooooooooo well worth the drive. Gout is a disease that once you get it diagnosed and start treatment, which by the way is a daily dose of the medication Allopurinol, which is not at all expensive, as well as pain management, and once you get it under control, you don't need to be running back to the vet all the time to treat it.
An experienced reptile vet should do both an x-ray and blood work to diagnose or rule out gout, and these 2 tests will also diagnose and rule out a host of other conditions, like an infection, a muscular-skeletal injury, nutritional deficiencies and the diseases and conditions they cause like MBD and Vitamin B1 deficiency, etc. DO NOT JUST SETTLE FOR AN X-RAY!!!! SHE'S LARGE ENOUGH TO HAVE A SIMPLE BLOOD DRAW TAKEN TO RUN A FULL BLOOD WORK PANEL, AND THIS IS THE ONLY WAY TO DEFINITIVELY DIAGNOSE GOUT!!! I'm telling you this because a lot of "exotics" vets, general vets, or vets that don't know anything about gout in reptiles will often first take an x-ray, and when they don't see any Uric Acid Crystals in the dragon's joints (which is most likely the bump in her left knee, but they don't always or even often show up on a regular x-ray), they automatically rule out gout the problem, then they just prescribe a medication for pain and swelling and probably a totally unnecessary antibiotic (how do they know they have an infection without blood work?) and send you home, telling you it's just an injury and she'll be fine after a week or two. Then the poor dragon just suffers and suffers, deteriorates, the unnecessary antibiotic makes them even more sick, and instead of getting a jump on treating the gout, the gout is now so bad it's breaking down their muscles and the poor dragon can't even move. So yes, you want an x-ray, but you also must insist upon blood work to check her Uric Acid and her CPK, those are the two levels that usually diagnose gout, and also you want to know her blood cell counts. And always ask them for a copy of the blood work results to be emailed to you immediately when they get them.
Until you can get her to the reptile specialist, there are a few things you can do to help her feel better. Tracie, one of the moderators here, is an expert on Gout in dragons, so hopefully she sees your post soon and chimes in with her recommendations, as well as whether or not she agrees with me on a diagnosis of gout. The usual things that help relieve some of the swelling and pain of gout are #1) Giving her Black Cherry or Tart Cherry Juice or Extract, whichever you can find. Usually you can find Black Cherry and Tart Cherry Juice at most health-food stores, as well as grocery stores that have a large organic and natural foods section, like Wegmans, Whole Foods, Harris Teeter, Trader Joe's, etc. If you give her a few ml of the Black Cherry Juice or Tart Cherry Juice every day it should help to relieve some of the swelling and pain. #2) It's extremely important that you keep her very well
hydrated every single day, as gout is very hard on their kidneys. As the uric acid builds up in her body, the kidneys go into overdrive trying to get rid of it, and this can result in kidney damage. So the more fluids she takes in to flush out the Uric Acid the better. So if she drinks out of a bowl make sure she has a bowl of water at all times, if she drinks during a
bath be sure to
bath her every day, and if she does neither then you'll need to give her a 2-3ml of water or unflavored Pedialyte a few times a day. You can drip the water or Pedialyte on her nose and let her lick it off, and if that doesn't work you'll have to use the syringe forced-fluids method, which is really easy actually.
If you fill the oral syringe with either the water or unflavored Pedialyte first, and this is also how you give her the Black Cherry or Tart Cherry Juice, then use the tip of the oral syringe and insert it under her upper lip at the side of her mouth back towards her ear. Once you have the tip of the oral syringe under her upper lip on the side of her mouth back by her ear, slowly slide the tip of the syringe up towards the tip of her snout, keeping the tip of the oral syringe under her upper lip the entire time you're sliding up towards the tip of her snout. Once the tip of the oral syringe reaches the tip of her snout, she will automatically open her mouth, I don't know why they all do this but they all do, lol. Be sure to have your thumb on the oral syringe plunger the entire time, so that when the tip of the oral syringe reaches the tip of her snout, you're ready to VERY GENTLY push a small amount of the Cherry Juice/Water/Pedialyte into her mouth. You don't want to push a lot of liquid into her mouth at one time, or "shoot" it quickly or forcefully into her mouth, as you don't want her to aspirate it. Once you do this a few times you'll be able to judge it easily. Let her swallow the liquid, then just start over again, inserting the tip of the oral syringe under her upper lip, on the side of her mouth, back towards her ear...just keep doing this until you get the necessary amount of fluids in her. Works very well, and is not at all stressful for the dragon or for you as a lot of other methods are.
The other thing that really helps a lot with relieving the pain and swelling of gout is a supplement called Serrapeptase. Serrapeptase is a naturally-occurring enzyme that is a wonderful anti-imflammatory and pain reliever, and people with beardies that have gout swear by it. You can either order a bottle of Serrapeptase capsules online (pretty inexpensive) that you can open up and dump out the powder and then give her the correct dose, which Tracie can help you with, or you can order her live Silkworms and simply feed them to her as her live feeder insects. Silkworms contain a large amount of Serrapeptase inside the inner-lining of their intestines, and they are a very healthy feeding for bearded dragons anyway. So either way, Serrapeptase is a must for a beardie with gout.
Tracie can make her recommendations and give you her advice when she sees this, like I said, she's the gout expert. What I do know is that most beardies who are first being diagnosed with gout and are experiencing a lot of pain and swelling to the point where they can't move, seem to do very well once they are put on the appropriate dose of Allopurinol. She'll have to be on it for the rest of her life most likely, but as I said it's a very inexpensive prescription drug, and people often take it for a variety of reasons, but gout and kidney stones are the most common, and it's available in a cheap generic form.