Am I a bad and selfish sister for refusing favors?

My sister asked me to take my niece to school. She’s in private school and lives far so there are no buses. I figured to do it even though it was all across the city, waking up very early at 6am, fighting traffic, and then sitting at a coffee shop for 2 hours waiting for my internship to start….

She goes to business meetings out of town quite a bit or she’s too busy to do it for some other reasons.

Anyways, it’s becoming more and more common that I have to take her. It’ll be every 2 weeks or so. I know it doesn’t sound like a lot but it is such a hassle to take my niece to her school.

In less than 3 months I’ve already taken my niece to school 4 times already. I was just asked to do so again and she’d give me gas money (I refused gas money other times but she put it in my purse) but I don’t even care for money, I care for my time.

I explained to her that I’m really tired waking up early and waiting for my internship and if there’s anyone else that can do it. If not, I’ll do it. I also explained I don’t mind doing it from time to time but if it’s possible to alternate the responsibility between me and someone else then I’d appreciate it.

She has her daughter’s friend’s parents, my older sister who has her own business, my parents, etc. But I guess she relies on me because it’s “easiest”.

It seems like people tend to ask ME favors like pick them up from airport, drop them off, etc. etc. because I’m too nice to say no possibly. I feel like a taxi driver.