Your goal is to approach the alpha of the group this will validate her status within the groups hierachy, and it is her who decides whether the group will accept you.
You can elicit who the alpha is by the body language of the girls around her, generally they will make eye contact with her after making a statement, suggestion or question to see how it is being received. In the past I have approached with the line "are you girls all together?" When she says yes or why reply "because you're the most (pick a desirable trait not involving looks) of the lot of you which is probably why I'm talking to you" then straight after ask her a question this disables her auto pilot response as the cognitive process are re routed to answer your query. A question I like to use is "would you say you were a sophisticated woman as I need a female opinion on something?" she should say yes (nothing is 100%) tell her you have two different aftershaves on and can't decide which is the nicest (you have applied these earlier) ask her to pick one. She leans in and you get a bit of kino, the groups sees this and you assumes you have kino rapport (they don't know the real reason) so you're accepted into the dynamic. When she picks one of your fragrances reply "you like?" and point to yourself and nod. Thats a subtle subconscious nudge to imply she likes you.