Advice

Ok so I’m 17 years old my little sister is 13 this year she has had her first relationships she biologically isn’t related to me so she doesn’t really go into depth things like that that sisters normally talk about so here is where I need advice she is bisexual I thought it was a phase but I can tell she genuinely I guess likes boys and girls and I’m 100% supportive of it the advice I need is how to be there for her her mother pushed her away when she told her that she was bi and I don’t want to be like that