If you don't have a top-notch wingman on hand, you need to multi-task and play both the offense and defense position. That means maintaining her interest and also engaging the group so they don't drag her out of your arms. 

When you're warm and friendly towards the group, women will get the sense that you are a nice guy with good intentions (hopefully, they're right in their assumptions). This will become especially important if they decide to leave you alone with her. If your character seems questionable or you disregard their presence entirely, it won't be long until one of them shouts out "Vamanos, Jets!" Seriously, there might even be an accompanying snap and everything.

However, just a word of warning. While trying to entertain her friends, never make it questionable where your interest lies. Tell the group a good anecdote, but reserve your flirtations for your object of interest. Flirting with her friends will make you look like a jerk, and worse yet, might prompt her not-so-cute friend to call dibs on you. I've seen it happen. It's not pretty.