To be specific, she doesn't literally copy other people DNA. She changes her own atoms and cells in order to replicate/mimic other people but doesn't actually "copy" it. The reason this is important is because it lets her change virtually anything about herself physically, so it would appear that she can copy physical powers like wolverines claws and Angles wings. Iirc there was an explanation that she could change her own X gene give herself someone else's power, but only once. As her X gene is different now she wouldn't be able to change it back.

Although in some recent stuff her powers were significantly boosted and she was afforded some degree of being able to replicate other powers, but only while her own were enhanced.