Personally the easier way to have handled it would have been to let her audition and they would tell her rather bluntly that singing is not the career for her to pursue. Then you would not have been the bad person and she would have been given a major reality check before it was too late
NTJ. My real name is something only my grandfather and great grandmother ever consistently called me never by my nickname. Once they passed I no longer allow anyone to call me by that name. Even new employers are quickly informed I do not answer or respond to that name and it's been 39 years since they passed. So it's not like time has anything to do with whether you want to accept being called that name.
He is definitely trying to control you and isolate you under the guide of caring about you. Don't let him fool you or you will end up isolated and constantly gaslite while he does what ever he wants and controls you. These are just the first steps and usually they wait longer to show their true colors the fact you're only five months in and it's this bad is scary to me.