WIBTA for not giving my son’s ex-girlfriend a ride back home from college for winter break?

I have an 18 year old son that I share with my ex. My son just finished his first semester of college. He goes to my alma mater, which is on the other side of the country (United States) from where we live. A couple of years ago, he started dating the daughter of one of his mother’s best friends. She decided she wanted to go to the same school as my son and is attending the same college.
Since she left for college, her parents’ marriage has imploded. She also has apparently been having a hard time finding friends at the college. She started treating my son badly and this culminated in her kissing another guy. My son broke up with her after finding out. That was two weeks ago.
The winter break is about a month long. She had been planning to ride with my son back home (she does not have a car). I flew to the college to ride with my son in his car back home. She apparently assumed that my son was still giving her a ride because she asked my son when we were planning to leave tomorrow to drive back home. My son told her that she is not getting a ride. This resulted in her calling her mother, who called my ex, who called our son and demanded that he give her a ride. She has no other way home and the plane ticket is about $1200 right now (plane tickets in the US are a mess right now). He refused. My ex called me since I am here and demanded that I give her a ride since it is technically my car (I am the only person on the title). I told her I am going along with whatever our son wants to do.
Apparently, this is causing all types of issues for my ex and the girl’s parents trying to figure out how to get her home. AITA?