I definetly have issues with clothing for ex I can only wear one type of socks which I turn inside out because they are softer. I also only can wear tennis shoes. I think everyone is different as stated from here.
I do know for me that the more I stay away from a material the harder it is for me to adjust again. There are some things though I just can't tolerate and for someone else to purchase for me would be near impossible. When I have had a nicer outing like a special dinner to go to my anxiety does rise because I have no clue how I will tolerate the items I need to wear.
If you are helping her maybe do some pre online browsing. You may have to get a little creative.