How to understand if she is a lesbian

I (23m) like this colleague (22f) and I "fear" she is lesbian. I don't want to ask her directly because it would be too awkward. I had a chance at knowing more about her with time and finding out she likes these things: - engineering - anime - general japanese culture I met many gay girls with these interests. The other day I gave her a ride home but yesterday she said no, I hope today she says yes. I feel like being 16 again... We are both engineering students and like maths and physics, we compared ours lessons and she seemed a bit sad that we didn't have lesson in the same building at the same times but she is really caring about everyone like, not just sometimes but ALWAYS she is ready to do a small sacrifice just so that noone feels left out even if she is not the most extrovert person. She is genuinely the kindest person I have ever met, if I believed in paradise I'd expect to find her there