Here’s what I think
1- find out if your crush likes girls. If you already did this, them skip to #2. If not, then countinue. A way you can see if their bi, gay, pan etc is by bringing up the lgbt community to them and seeing how they react, idk if this will worked for you, but it’s how I found out my old crush was gay.
2- ask if they like anyone. If they honestly like someone else, they will tell you. If they like you, or don’t like anyone at all, they’ll prbly say something like “no, not really”
3- when you go tell her that you like her, don’t be like “hey whatitsfaces, I like you” or something. You should say something along the lines of “I’m beginning to develop feelings for you” because if she end up not liking you, it’s gonna make it easier for her to tell you if you say “develop” instead of “have”. It also might help save the friendship, since it seems like you aren’t completely in love with her.
See how she reacts in a group of people. If she tries to talk to you more, or glances or at you while talking to someone, she might like you