I agree with stepnstone. This is most likely due to age. I have a soon to be 11 year old flyer.
I thought of overgrooming as well but based on the pics that is unlikely. They will even ‘barber’ which is pulling their own hair. This can only be done in areas they can reach like the abdomen, arms, legs, etc. They can’t reach their back. I almost wonder if it’s fungal or even a mite but without a definitive diagnosis I would be reluctant to blindly treat a 12.5 year old flyer. You might want to change out the bedding just in case.
Of course, a little extra calcium won’t hurt but I wouldn’t overdo it either. Dusting the food she likes with a little calcium carbonate powder would be fine. You could even give her a fruit flavored Tums (no artificial sweeteners). Some will nibble on them.
Bonzai just loves navel oranges. When I give him a tiny orange wedge, he will clean it and leave the peel. He likes the sweet ones. If it’s a little tart he will leave it.
Some will eat full fat yogurt. Both my boys like avocado. These are just some healthy ideas for added nutrients. Clearly, you have been doing A LOT right to have a 12.5 yo flyer so I’m not criticizing your diet at all, just offering some ideas that my boys like. This bad mama has not given it in a while (he’s getting it tonight) but Bonzai actually loves formula. He will drink warm FoxValley out of a bowl. The 32:40 is recommended for flyers because of the extra protein but he will also drink the 20:50 as well. Speaking of protein, does she eat meal worms? Flyers need worms for protein. My boys prefer Wax worms.