Sudden death of our Beardie! Need help

Hello all, I am sorry if I have posted this in the wrong area or did something wrong. I've never really used a forum besides the Ratshack, as well as I am using my phone for this.. Please forgive me ;3;

Now on to the post.. Well unfortunately I am very deeply sad to say that our Beardie Ridley died this last Thursday, April 19th 2017. She was my boyfriends pet for only four years(she was a baby when he got her) So she died super young and very suddenly. I loved her with all my heart for the year that I was with her. But I am so restless with how it all went down, and would like to know just what killed her in the end?

The set up:
40 Gallon exoterra tank
NO substrate that contained small pieces such as sand.
I'm not quite sure what bulbs we used as we had gone through 3 different brands during the week she was sick.

What happened- We woke up to see our baby not quite as hyper as usual, with a little bit of an eye problem. We washed it out with saline for a day or two before making a vet visit as it seemed to be getting a little better. But then she rapidly was losing weight. She was tiny, so we made a very quick emergency vet visit. And was given eye drops, antibiotics of some sort in the form of drops, and food to force feed her as she wasn't eating at all. We did this as planned for another couple days, with no improvement(I know they heal slowly but we were so worried!) so we called up the vet and was told to give it more time before coming back. Well things started looking brighter and she seemed to be doing much better, no swollen eye, gaining weight. But we woke up for work and saw our precious baby lifeless.. She seemed to have blood in her mouth from what I could tell but I am not sure.

I only have a picture of her eye from when we went to the vet.
Her eye was pussy almost, slightly swollen.
I just don't know what went wrong and why it all happened so quickly and I want to put my mind to rest.

Any questions to help answer what happened, I'd be more than happy to answer to the best of my abilities.
Thank you guys so much ahead of time ;3;

I am so sorry you lost your baby, they sure have a way with getting into your heart in a hurry.
Four years old, tells me it wasn't anything you did and, most likely couldnt have stopped it (they are very good at hiding illness and pain). Usually by the time you dicover that there is a problem it is already to late.
Just know you both did what you could for her, you loved her and, she loved you back in her own little way.

RIP Ridley

Obvious she was much loved and given the best care you could. More than likely she had some kind of birth defect that was not picked on at the vet ( some are hard to spot ) or perhaps an abscess in her body cavity associated with the germ that created the eye infection and had been sick for some time , they little buggers are experts at hiding the fact they are sick until they are so sick they can't hide it anymore.
I really feel for you , and can relate 110% to how you feel.

I lost my Rex (about the same age) a couple of weeks ago very very unexpectly and suddenly, she was fine in the am , and had a great meal and a few superworms as a treat, and was fine until about two hours before her death.
Suddenly she was behaving like she was trying to chuck up some of her food and it was rapidly downhill from that , and she died on my chest while I was trying to keep her breathing (giving her CPR until her lungs collapsed and she no longer show any responses (indication life).

If it helps, have good cry , often and as long as possible. I know you loved Ripley.

In my case my two young beardies Peppa and Toothless and my old BTS George and Mildred have kept me busy and helped , and my wife has also been a great great helps.

Thank you guys.. :c She meant a lot. It's amazing how much personality they can really have. In my case, we have four rats as well right now and they seem to be helping my boyfriend and I. Two of them are trained service pets so they help as much as they can.

I wish we could have noticed earlier or did something different. ): We gave her a full burial and a proper send off, and planted some flowers over her. She will surely be missed by anyone who met her <3

EDIT: Sorry I accidentally hit submit. But I am so sorry for your losses as well. These little guys really do touch your hearts! They are very sweet and curious creatures.