Sitting around waiting for the right moment is how you lose out on great opportunities. Either create that moment yourself and just tell the person or don't bother and just move on.
Worst case they say no and turn you down and ignore you forever and ever and ever, which at least is a closure so you can move on to better things and not dwell on a "loss", or be in a state of limbo of not knowing. Maybe she'll say no and just be friends, at least she knows your feelings toward her.
Don't dwell on the thoughts of what if the friendship is ruined, what if she never talks to you again or what not. Think about how good things could be if she said yes and just go for it. Don't live a life with regrets!
I had a crush on my boyfriend for months before actually making a move on it. I was sooo shy and absolutely terrified of him!! We were co-workers and I took any opportunity to impress him...I brought yummy things to work that I had cooked (only to find out later he was a picky eater and didn't like anything I brought, lol), I hung out at mutual friends' houses all the time just hoping he would be there, and finally got the courage to start talking to him - turns out we had a LOT in common! We went to a concert together (as friends) and about 2 weeks later were dating. It's been almost 5 years now and we're still going strong and very much in love. So, even if you are too shy to make a move, don't give up hope, the right moment will come along if it's meant to happen