I know this is super obvious, but you just have to talk to her. She’s not going to swear off sex forever. Maybe something happened during the first time that has her worried or feeling tentative about it. Maybe she felt like it was overwhelming? Maybe she didn’t enjoy herself as much as she wanted to…
It could be any number of things. Don’t jump to drastic conclusions. If you really do care about her and you want this to work out, give it time and that means as long as it takes. Of course you don’t want to be celibate, but you have to be willing to compromise here an give her time. There’s something holding her back and you have to find out what that is.
I would just dive into it. Tell her how much you want her and how beautiful and sexy and amazing she is. How much it’s killing you to not be able to touch her.
Ask her exactly why she wants to take it slower.
See what she says. If she still can’t really find the words, then ask her if there was something that happened that first (and only) time. Did you make a mistake? Was it too fast?
Did it feel overwhelming or out of control?
Was it not good for her?
(Follow that up immediately with reassurance that it’s okay if she didn’t because it’s a work in progress and you want to do whatever you can to learn about her and make it the best experience possible.) Be completely honest and humble.
Express how much you want sex to be good for her, for it to be something you guys share, and if something got messed up the first time, wires crossed, whatever it is, let her know that she can tell you about it and you’ll understand. You’ll do whatever she needs. Don’t accuse her of anything, just entreat her to talk to you about it and show that you won’t judge or get defensive or fly off the handle if she says something you might not like. (Not only do you show that, but you also need to DO it.)
Show her that you care about her, explain that you’ll go at her pace no matter what but you just need to understand more about what’s happening inside that head of hers. Be open, listen, and be a safe place for her. You both have to establish a base of trust and honesty with each other. Everything else will fall into place after that.