Is it okay to tell my friend I don't want to drive her home
Why wouldn't you give your friend a ride home?
I like to drive my car but I don't want to waste my gas on her.
Refusing to take your friend home just because of gas seems  a little rude. Maybe your friend can help you pay for gas and that would be a sound compromise!
I just wasn't feeling like I should be responsible for her like that.
Some gas money sounds like the best option here then. I am sure your friend wouldn't mind helping out a little since you are also helping them.