If you have absoultely no window to game her then just simply say 'me and a few others are going for a drink after work (obviously on a day you're not working, if as you say you finish earlier), I'll see you there. Don't be AFC about it just assume she's coming.
You've probabaly 10 minutes to game her before she asks where the others are, by that point you're either in or out and lets face it you were out before so what have you lost. One word of warning you need confidence to pull this off, if your games weak or you lack confidence she might just see you as a guy that tricked her.
A far better option is to day gamer her at work if the opportunity presents itself.
Good luck
And if you blow it where do you work? If she's as good as you say she is I might pop in for a meal.