your going to college. your mom doesnt need to take you.

Valid a point though that is, you don't know where the dinner is, nor the contents of his wallet. A paid ride may not be an option. Although if the sister is going, and is getting a ride from the (despicable in my opinion) mother, he could just grow roots in the car. Either she takes them both, or neither goes. It's a tad childish, but since the dinner is for him anyway, i think it works out.

This will be the most important Uber of your life.

You get your scholarship and she gets a dinner. Fair enough to me.

You should bring your sister as your guest, so you can rub it in her face that you’re better than her!

You know who the favorite is now.

Tell your mother that the college is giving your sister a participation trophy at the dinner as well.

Your sister should be telling your mum that she’s happy for you and that it’s fine.