Some general stuff
1. Try not to focus your energies exclusively on just one girl. Especially right at the start of a relationship. You don't know each other that well, and she might be crazy or stupid or something, even if she is hot. Be interested in finding out about her, but it's better to verge on the side of being a bit aloof than too invested (i.e. NEEDY). In practical terms, that means waiting 2x as long to answer her texts and she takes to reply to yours, not always being available or changing around your schedule to fit hers, and waiting a day or two after your last date to tell her you had fun. Just to keep her thinking about you and wondering if you had as much fun as she did
2. Don't be afraid to escalate too quickly. By building sexual tension and kino escalating rapidly, the only thing you really risk is her saying "slow down." If you don't do anything after a few dates, she'll start to wonder if she's not attractive to you, or if she said the wrong thing, or (more likely) that you're a pussy. Be the guy she wants to fuck FIRST, and then show her that you're boyfriend material SECOND (if that's what you're looking for). That means kino kino kino, seductive eye contact, deepr voice, and turning the conversation onto sexual topics.
3. Don't be reactive. Better to ignore insults than to rise to them.
In this particular situation, with the information I have, I would say this:
She lost attraction for you because you gave off the classic "nice guy" vibe. You seemed very emotionally invested in her, but you were too chicken shit to escalate. She gave you some past relationship bullshit either as backwards-rationalisation in her own mind, or to give you a nice reason that wasn't "sorry you're too much of a pussy."
Calling her a coward = MASSIVE FAIL. She's not the coward, YOU'RE THE COWARD. Be a MAN and grab her, pull her in, tell her she looks fucking sexy tonight and you can't wait to do all kinds of dirty things to her. You know she wants you, and you want her. SHOW IT.
You're unlikely to be able to get her back, but my advice would be to apologise for calling her a coward, tell her that you guys get on and you're interested in exploring that with her, and when she gets over her past relationship issues, to give you a call. Then go out and game other chicks and forget about her. Who knows, she might get horny one day and get back in touch. If not, fuck it, it's one girl.
If, after 2-3 weeks you still wanna try and give it another shot, you could invite her out with friends, and have her see you in the company of other women who you are being flirty and sexual with. Then you could re-game her from basically square one and be very flirty and sexual with her too.