I drive my younger sister and her friend around but starting to think I shouldn't?

My younger sister has a friend. She is a little bit of the princess type she's 20 and my sister is 19. 

I'm 22. I drove them a lot of places like the beach and the mall, park, the city, and we would go shopping. These places are usually am hour drive. 

But a lot of the time when I'm driving them she keeps looking at me like I'm old. And keeps looking at me a bad way. A lot of the time when I talk to her she has this expression like why are you talking to me. When I do nice things like pay for gas or food I see it as being nice, but it's like she's thinking in her head "yes, use her for gas. "

Instead seeing it as being nice she seems to see it more as me being a stupid girl she can use. It's extremely annoying. 

She just babysits for her mom so she doesn't have a lot of money and my sister quit her job because of bullying. 

I was being nice because I was sometimes my sister could hang out with her friend. My sister's friend was having trouble at home and her mother was telling her she might kick her out. 

But I'm getting at my wit's end because I don't like driving someone around if they are like this. I'm thinking put my foot down and tell my sister that she can tell her friend to pay for gas and do the driving. 

Her friend didn't want to out miles on her new car and pretty much won't drive her anywhere.