Why?

We are supposed to go out of town for the weekend. My mother says to me, hey- why don't you ask my homegirl to ride with us. I ask, and she's down for the trip.
So today I say to my lovely mother, "Mother, my service engine light is on. I am going to get it checked out, and depending on the problem and how much it costs me to get fixed are you willing to pay tolls & gas?" Her response: "Well, isn't Shonda going? Can't she help out with gas?" I'm confused, didn't we invite her to go on a family trip with us? Is that trifling or what? I mean, hey, come and visit my family with me, but I need you to help pay gas. I could see if she offered to help pay some expense, since she is like family anyway- but to expect or demand she split the cost is just GHETTO! My mother has some serious issues
She's starting to make me regret my decision on negating my other "trip" to take this one..... I can't even revise my weekend. I think he already has plans