I'm pretty sure it's safe, it was recommended to me by the President of our Parrot Club and I trust her not to recommend something dangerous. I got the cage set up tonight with all her perches and toys. So far she seems to be enjoying the larger space. I'll be keeping a very close eye on the painted spots though to be safe, and I'm going to double check with her vet on Monday whether she has any other recommendations. I'm keeping her smaller cage so that if I get together the funds to get the powder coat redone she has a place to stay while that happens, plus when I move later this summer it'll probably come in handy for the transition. Here's a photo of her new cage set up.
Just be very sure that paint is bird safe. Even if she doesn't chew the cage bars, she will still use her beak on the cage to move around (at least Timber does).
Auri is blessed to have you, and I'm so glad you decided to take her! You've seen first-hand the rehoming situations and know how time, labor, and emotionally intense dealing with a grey can be. Good luck, God bless, and welcome to the forum!