Can you talk to her and tell her what you've told us here about how the dog needs more than she's getting in the way of attention? maybe you can "offer" to take her into your home for a while to "train" her, since your sister is "so busy", and your sister will loose interest? Sadly if you imply your sister is not taking good care of her she may get ticked and say no, but if you can make it sound like it's a good thing for her (your sis), maybe she'll say yes?