Whoo dang! That's a tough question. Let me put it this way. You CAN tell her without being slaughtered, but first you must learn to walk on water.
If she is that much against gauss it may be best to keep mum
If you really fear for your safety, don't tell her unless you're not living with her and only when you're in a serious, committed relationship with a man. Otherwise, there's no reason for it.
Convince her it's not as bad as her marrying your father?
I doubt the Bi part would make her kill you. Fear of no grandchildren might. Being Bi means hope for her.
wait until you move out, then tell her over the phone.
Don't, that is your business and none of hers.