I have a younger sister who's been a bitch to me for as long as I remember. I've never heard a nice word from her. In fact she only interacted with me whenever she needed something.

My last bright memory of her was from about 10 years ago when my parents gave us tickets to some show, I was driving and got lost so we've missed first half. So my sister got mad and straight out punched me in front other people. I've never heard any apology or anything so since then I've stopped any interaction with her.

Now she's coming to my city for a vacation with her boyfriend. And I've been getting calls from my mother to come drive 2 hours to pick her up from the airport and let her and her bf stay at my place so they can save some money. My sister wouldn't even bother to contact me herself. I've been feeling really uncomfortable being their tour guide and free place of residence and possibly free meals (since I am making good money and she's broke as shit). My mother has been guilt tripping me into how 'she's my family yada-yada and why I am being such an asshole'. But it just doesn't sit right with me to help a person like that regardless whether I am related to her.

I dont think I should help her, so what would be a diplomatic way to say no here? And yes my mother knows everything I've described here as I've told her many times, but somehow it's on me to make amends.