help me please

My little sister came out to me over Christmas I am the only one who knows that she is bisexual but but she mainly likes girls but with the way her religion is she scared to come out for mom... how do I help her come out to her mom about her sexuality!! I support my little sister hundred percent no matter what it is no matter what she wants to do I have her back no matter what!! But she is so stressed about it and it makes me sad seeing her like this !!! Help please !! Keep your rude comments to yourself please