Why are 1st borns so stubborn -rant and ??

My oldest daughter is 21. She lives at home and has a pretty charmed life. Ask her and she has the worst life ever!!!!  Ok so my hubbys grandparents gave us a free van. Yea it's old, yes the air doesn't work but it's really only hot here about 6-8 weeks. She has done. Nothing but complain about the free car that she drives and doesn't have to pay anything for. She does pay the 68$ car insurance and has a full time job. Now she is not rolling in the dough just yet but holy crap if she doesn't think she is a freaking millionaire. She wants to move out this fall. Mom and dad want that too😂, but she wants to go buy a 12000$ car when she is at best pulling in about 800$ a month give or take. She will have saved around 2000 by middle of next month. By the way, the dealer ship wants 2700 down and I believe a 300$ car payment monthly. Not to mention the full coverage car insurance that is 200$ a month. My advice is for her to buy a cheap little used car and drive it for a year or more. Keep saving$$ til she moves out and get on a budget and after a year or so use the cheap little car as a trade in. This way for her 1st year outside of my womb I mean house, she won't be strapped for cash. Can still have the independence she wants plus have fun like most 21 yr olds do. But why listen to mom. Does anyone else have a head strong kid like this? Any way to help her see the light. She is so stuck on the "appearance" that she can't see the bigger picture.  I really don't know how her head is stuck so far in the clouds. Her friends are the same way. Maybe it's a generation thing but dear god I hope not!!  Now I will say my parents are rather rich. My husband and I are middle class so we get by. So maybe she needs to just fall on her ass but I can not afford to bail her out if she gets over her head. Back to the title, my brother, aka the golden child. Was and is the same way. Except my parents fixed his screw ups. Even has basically raised his 3 children ( all from different mommies). Ok I'm gonna stop ranting. But if anyone has some real advice not catty ba comments please let me know. Attitude need not apply as I am up to my eyeballs in that crap lol