Are you supposed to turn down the money somebody offers you to do them a favor that you don't mind doing?

I drive for Uber part time. My dad's girlfriend of a year (whom I really like) told me she'd pay me to "Uber" her to the airport. I don't mind doing the favor and honestly, I could use a little bit of money, but I would do it even if she wasn't paying me.

Am I supposed to tell her that she doesn't need to pay me? I assume that she will insist that she does pay me. Do I push back again or just let her pay me?

My mom is Polish and she told me that you're supposed to push back 3 times before letting them insist on doing something nice. I'm in North America if that gives context for the culture that I live in, as apparently culture dictates how to handle this