Well if you have mutual interests. You can send her private messages. Just share a song you like, and ask her if it makes her feel the way you feel or something.
Make sure you seem INTERESTING, but not THAT INTERESTED.
Also, I don't understand why you didn't private message her in the first place? She asked you to be her "fake boyfriend" to scare away those guys: this gives you a 1000 reasons to make jokes about this. You did it in public, and thus got hijacked by a cockblocker. You should have done that privately, and roleplay in the message. I'll give you an example:
You: hey Sally, wow, I really felt like a bodyguard that night haha. So whatsup?
Sally: haha, yeah I bet.

Well, today i... blablabla
You: Cool! You know what, next time we go to a game, I'll be wearing a bullet proof vest and a gun. It will complete the look for me

Sally: awww haha. You're such a funny guy.
You: thanx

, but seriously, I enjoyed meeting you and look forward to talking to you again the next game. Are you with me on that my little damsel in distress

Sally: Heey, yeah. I enjoyed it too, and am looking forward to it. haha. X your damsell in distress. LOL
This is how you can actually facebook-message your way into her bed so to speak...
The point is, you closed her. But you have got to keep her engaged on-line. Not every day, just little funny things. Don't send a message if you have nothing to say, or nothing to ask. So no: "hey I'm bored, how are you". shit like that. You can do that when she's your girlfriend.
Now, the whole idea is this. You want to get her prepped for the next game. The more you "let shine through" that you're an interesting guy, that you share interest, and that it will be fun to meetup and have adventures together, the more she will be looking forward to YOU instead of "the game" or "the night".
If you have doubts about this, or think this is too difficult for you, you can also just wait until you meet her again an take it from there. But always work on your texting and facebook experience. It can brighten up a girls boring day if you're good at it. And it will definitely stimulate her subconscious into thinking your a cool guy. Even if you have a bad hair day, when she meets you again.
Good luck! I hope this helps.