I think this sort of dilemma is best handles using Mystery Method. With this in mind, I'd recommend opening the whole group and making friends with the guys first, whilst mostly ignoring and negging the target. This way you'll not only get peer approval and be accepted into the group (thereby raising your value) but also, through some light negging and ignoring of the target, lower her value and get her clamouring for attention.
This way, when (after 5 or 10 minutes engaging the group) you say "do you mind if I borrow your friend [the target] for a while? I've kinda been ignoring her", they're more likely to approve and allow you to isolate her...and obviously here you can escalate easily.

I think the key is befriending the guys, especially the AMOG. If you do that, the girls will warm to you very easily.

Hope this helps