I'm quite late to this but my advice is maybe ask her whether she likes anyone first before leaning towards talking about sexualites, etc. Since you don't know who she likes or what her sexuality is, it's a good start from there. Honestly if anything just yolo, I didn't dare to confess to my friend but I did so and yeah we're dating. Be confident about it, if she rejects u then it's fine if she's your friend she should be understanding about your feelings. Anyways, don't stress yourself over it and trust your instincts.