I dun think you have mentioned much about your aunt's relationship with your uncle but I do feel like its her parents relationship that is affecting her so badly.. kids are very sensitive and they pick up more than we can imagin!!!
she needs a lot of attention and a happy home (not yours but hers where her parents treat each other with love and respect).
her parents have normal relationship with eachother, but not as open or great as one could expect. when her father is at home, he is usually watching movies. he doesnt take them out neither plays with them. but i can not say they have unstable marriage or relationship. we ask them to go out with us as a group but they dont. so we take her with us. but she grew up in that environment.
we tried to talk to her parents to change themselves, spend time with their kids, take them out, and enjoy life with them. but they dont listen.