Im pretty sure she will get the message at some point when you two dont end up married.
It depends on the friendship and how deep it was. If you two were very close, then maybe talking it out is a good option. Please dont say things like “Im not interested” or something.
You can tell her you are already interested in someone else, not ready for marriage, gay, whatever.
If you’re not close to her…leave her alone. She will get it.
