Need help with scared conure

[GallifreyTheMango]

I rehomed a sun conure almst 2 years ago. She is almost 14 so for 12 years she was kept very wild until the flock she was with kept trying to kill her. She has bad balance and can't fly well. So she was housed in a small cage. I offered to take her. We have built A LOT of trust and she takes things from me and even does basic target training really well. Here's my problem:

She won't let me touch her and she can't reach all of her pin feathers to preen them. I've done minimal grooming by catching her and holding her in a soft towel so she can chew and grab it but when I try to get a hold of her so I can do her back I fail and she wiggled out of my grasp. Today I managed to keep her pretty still on my lap by putting the towel over her but I can't get the sheath on her feathers off. I've tried a tooth brush and that didn't work. I read you have to be careful because they are super sensitive so I'm not sure what to do. I don't want to cause her any more discomfort or stress than I have to. I think she likes a pit of scritching on her head but it doesn't last long. She has over preened on one shoulder (not bad but enough of a teeny bald spot to notice) and I think its because she can't reach the darn pin feathers that are annoying her. Any suggestions on a way to get the sheath off?

 

[Roo1130]

When my sunny is molting i help him with his new feathers by ever so gently rubbing the new growth between two finger nails. He wasn't always agreeable to the help but i've learned the balance of how gentle he needs me to be. It's been trial and error. I actually didn't know i could help the little guy out until my vet showed me and now he rather enjoys it and grooms me back lol

 

[GallifreyTheMango]

That's what I tried. I think maybe I was being too gentle with her larger ones on her back and there was no progress so she was getting agitated/impatient. Thanks!