It takes a fair bit of confidence to be flirty, so at least you've got that down to an extent. Honestly I find it extremely hard to get close to anyone when I'm not alone with them, and sometimes my paranoid thoughts just leave me unable to communicate with people on there own, which is probably the reason why no one likes me at the moment.
If I had to give you some advise though, I'd tell you to find a way of getting her on her own without it being creepy. The best solution here would be to just ask her out face to face or ask her if she wants to come over to share a common interest with you (watch a movie, listen to music, ect). You're going to have to get talking to her about what she likes, and see if there is any connection there man... thats all I can think of anyway!