It all depends of how accepting your mom is in reality.
A good test, once some LGBT stuff comes out so as to start the conversation, is to ask her what does she think of homosexual people (do NOT
specificy lesbians); ask her further if she would mind someone if someone in the family turned out gay, and if she doesn't, stop talking about LGBT stuff the moment you notice the disapproval, and if she does approve sincerily and verily, then come out eventually.
I literally did this with my mom, and I seriously expected her support for gay people insincere, but at the end she accepted me.
Nonetheless, have a backup plan if things get very unexpected and you might have to get out of your mom's house.