(((((Wisewoman)))))))
You're doing so much by taking care of your adopted daughter and I know you want to help her sister and her baby too but don't forget about your needs too. This is probably putting you under a lot of stress so I hope you take a few moments out to treat yourself well.
Remember to tell her that there's always thrift stores. They're great in a pinch. Know of any thrift stores you both can raid for her and her baby? And for the other stuff you can't buy at a thrift store, can she get help from a community resource center? How old is she?
I bet you'd like to take her and her baby in too. Be careful not to take on too much. (((((Wisewoman))))))