Since you have her number, here is what I would do:
Try to build up some attraction through txt game. If you can't talk her into meeting you alone, make sure that the next time you see her, you are not in charge of the group, then hopefully, you will have built up enough attraction over txt game, that you can easily Isolate her enough to really start your game. One helpful technique, would be to develop some sort of little inside joke, or pet nickname for her, over txt. That way, you have a trigger that you can use, to bring her into a one-on-one conversation. Even better, you can lean over and whisper it into her ear, and immediately grab her attention.
Obviously, this doesn't answer you larger question. I don't think you can ever really game a specific woman very effectively, while playing host to a large group. However, while you host the group, you have all kinds of opportunity to dhv yourself, and show that you are a fun guy, which counts for a lot. Later, you are less likely to run into near as much resistance when you want to hang out with one of the women solo.
As always: Advice is worth what you paid.