I know several people that feel similar to your partner – that being trans is trendy or a phase that one grows out of. Decades of personal experience tell me they are mistaken.
I knew I was different when I was 4. Deep down, I’ve always wanted to be a girl. Those feelings came and went with cycles of exploration and purging. I’ve lost count of the times I tried to be someone I’m not meant to be. It doesn’t work. 6 years ago I got real and admitted I’m trans. I wish I’d done it 30 years sooner.
I know this is difficult. You have a daughter that needs your acceptance, support, and unconditional love. She is the only person that can decide if she’s following the right path. Allow her to be herself. And be honest about the challenges she will face. Some people may refuse to accept her. She may be bullied. She may face discrimination. Tell her none of that diminishes who she is. Help her build the confidence she will need to thrive.
I wish you and your daughter only the best. Emily