how about taking her shopping to help you choose socks and underwear for her? maybe by involving her and giving her some say over the decision she will feel happier about wearing them - maybe choose some with her favourite cartoon characters on or something. rather than buying standard briefs maybe there is somewhere that sells the short type underwear - just thought maybe these will be looser / more comfortable. and how about fluffy socks that just have a thin band of elastic at the top? i have some socks that feel too tight at the top where the elastic is - a small snip with a pair of scissors can help.
sorry i don't know if this is much help at all or if they're things you've already tried. Other than that i'm not sure what to suggest.
