First off, I do not want to generalize. Each person is different, and what might help me, won’t necessarily help someone else.
When I realized that I was bisexual, I was extremely confused and conflicted, as, although I was a staunch supporter of LGBTQ+ rights, I never thought that I myself could ever experience attraction to people of the same sex. I did find myself feeling much more attracted to one gender over another at times.
When I first was trying to figure things out, I ended up exploring much more my attraction to people of the same sex, something I never had ever dared to do before, due to how supressed I kept those feelings.
First of all, I would recommend giving her some time, and not expecting an answer right away. It took me months and months to figure it out, with me thinking, nah, I have to be straight, to nah, I am a lesbian, to I guess I’m bi, before the cycle would start all over again. So just let her know that you are always there for her, that you love her, and offer to be a listening ear. If you think you are up to it, and if she is okay with it, ask her if she would like to talk about her attraction to people of the same gender, and of her attraction to people of other genders, including whatever gender you identify as. That way maybe it would result in her not feeling as if she has to keep these feelings buried, or suppressed.
Also, realize that being bisexual just means to have the capacity to be attracted to more than one gender. It doesn’t mean it is necessarily equal. Just because someone may be generally more attracted to girls than guys, does not mean that if they end up in a relationship with a guy, it is any less meaningful, or sincere. After, some people may prefer brunettes over blondes, but it doesn’t mean that they do not love, or somehow love less, their blonde partner.
Most of all, just tell her that you love her, and want the best for her, no matter what. If she ends up realizing that she only loves you as a friend, make sure neither of you feel forced to keep this relationship going, and see if you can remain friends. Tell her that she shouldn’t feel pressured to figure out how she feels immediately, and, if you are up for it, she can talk to you about it.
Just be open to conversation with her, especially in a manner that reaffirms that it is okay to be attracted to people of the same gender, and that she shouldn’t feel guilty about this. Ask her what could you talk about with her to help her out. Also be open with her about how you feel about all of this, and know that no one can ever be a perfect partner.
Also, she if she feels willing to reach out to some online resources where other (qualified and trained) people could help her figure her feelings out.
Again, as I said earlier, I don’t want to come off as ( I apologize if I do) condescending or arrogant, as if I know how to solve all of the world’s problems, and that this is the way to go. Again, I am sorry if I just pointed out seemingly obvious stuff you already knew and tried, and this is all for nothing I really have no clue if this would help or not, but I hope it could. At best, it will just give you something to think about.
I hope it all works out.