What you know at this point are these two things: 1) although she may not be lesbian, she has told you that she is questioning, and 2) your online friendship is mutual rather than one-way. This should give you a green light to express your admiration and attraction for her.
You don't have to express undying love for her. Just tell her that you think she's cute or special -- whatever feels natural. Ask if she's open to seeing if there's a potential love connection or spark between you. Acknowledge that it's awkward and that you don't want to jeopardize your friendship but that you really like her and just had to take the chance in expressing how you feel. The only way you're going to potentially get to the next level is to take that chance! Good luck!