Step children.

I have been caring for my Aunt in my home for over 4 yrs. She has 2 step children that live out of state. One has never visited her and the step daughter will come on her Birthday for 3 days and at New Years for 3 days. My Aunt's b'day is July 6th so both visits are on a holiday. She has stayed in my home during prior visits and sleeps on the couch. This woman gets 5 weeks of vacation a year and yet she works it around a paid holiday from her job. She is a single woman without a lot of ties to any other family in her home town. She has always brought her dog and now wants to bring a girlfriend with her who has 2 additional dogs. My parents do have another home that we rent during the winter here in AZ, but now I am being asked if step daughter can stay there with her friend and 3 dogs. I feel she is stepping out of bounds by putting us in a situation where we do not allow dogs in the rental, do not know her "friend" and I do not know how to say no without hurting my Aunt'' feelings. I have never clicked with her step-children yet always try to be polite and welcoming. I have both Medical & Financial POA for my Aunt and was the one that stepped up to keep her from having to go to Assisted Living. In essence I feel I am caring for her and at the same time working for them. I hear myself resenting them and that makes me feel badly. I love my Aunt Dearly and would never want to hurt her feelings...telling her I can not accommodate her step daughter would do just that...I feel between a rock and a hard place.