Just like @immyelly1912 said. Just try getting a variety of people who are confident in riding on her. She doesn’t have the bond or confidence when others are riding her, so she doesn’t want to go. Before someone else gets on have them do some groundwork with her to work with her, gain trust, and show her that she has to listen to that person. Good luck!
my mare does the same, she's an angel (well as much as an angel a opinionated mare can get) and acts like a cow if anyone ever rides her! The best way to fix this I think is to get a variety of people riding her often.