I’m not sure you want to start getting comfortable touching her hair before you tell her - that may make her think you’re just using her to satisfy your sexual urges, which is usually bad for a friendship.

My advice would be to tell her you trust her as a friend and you want to tell her something because you think she’ll understand that you’ve been struggling with it. She’ll say of course you can tell me, then you tell her that you’re really attracted to nice hair on a girl and that you wanted to tell her that hers is really attractive. Then you can talk about it more and then, who knows where it could go

I have been in situations like this myself and it doesn’t always go how you want it, so best is to just tell her something as a friend and feel it out