Brand new Jeeps are so expensive! It was really nice! Maybe they had loan or something. I think her dad just really waneed her to feel special pb that day.

Then why not hire it for the day, they still had this car later on during the season.

Maybe just a minor plot hole

Her dad said he traded in the previous Jeep for this one and the payments were about the same, maybe just a little more. So he saw it as a small sacrifice to do something nice for his daughter. I think the reason they showed this is because we had to know that one of the reasons she killed herself had absolutely nothing to do with her upbringing or her family dynamics as she was in a home with loving, caring parents who pried to a degree (like when her Mom grabbed her phone and answered it) but also let her have her freedom to be herself and were willing to sacrifice/struggle to make her happy.