Jade,
If you are under 18, you have no choice then to tell her while you are still living in her house. If you are over 18 or your country's legal age, you can delay until you see a therapist. Either way you will have to tell your "liberal" mom anyway. My mom was conservative, but not overly so. She had her problem with mine at first, but quickly accepted what I am. Hugs!
Joelene