Almost every club has had/is about to have a used skate and clothing sale, so check Carolinas FSC or FSC of Charlotte - I think theirs is coming up soon.
We have racks full of dresses at our rink, left over from our sale earlier this month. I can give you/her the contact info privately if she's interested.
There are two women who make custom dresses in the Triangle area for a reasonable price, especially if she blings her own.
Other than that, SKS Sports is the best option for trying on new dresses. They sometimes have adult-sized dresses, so she could call the store to check before she goes.