Your care sounds good! A sixty gallon tank is very nice to have your beardie housed in, and is expensive, so good job! Your bearded dragon doesn't look skinny to me, but it is hard to tell in the picture. My bearded dragons' (I have 2) weights often fluctuate, so sometimes their skinnier and sometimes they're fatter. After they've defecated, they usually lose at least 20 grams, and food adds on about the same. My 17" adult beardie is 420 grams, and my 6 month old juvenile is only 210 grams, but he isn't skinny. So as long as your beardie is 350-600(600 if she's a giant) if she's an adult, or 150-350grams if she is a juvenile, depending on age, you're fine.
As for the greens, have you tried feeding them in the morning, before anything else? Sometimes they're hungry enough to eat them if you do that. If not, your bearded dragon will eat them eventually. If your bearded dragon is still a juvenile, she'll eat greens when her body needs them more. That being said, don't stop offering them. Still offer them daily, or, at worst, every other day.
