Well shes the popular girl.
She has all the guys around her the whole time.
Well I wondering is this good, first opening then saying something like so hey how many boyfriends do you have?
Just to in a way tease her

i don't think you should ask her how many boyfriends she has. I have found that if you don't bring up boyfriends, they'll forget about them. Just keep it easy going and keep her interested. If she's the really popular girl, don't let her think that. Make it seem as if she is lucky just to be talking to you. If she brings up a boyfriend at any point, brush it off and move on to the next subject. When I encounter a girl whom I just met and she says "I have a boyfriend" I simply reply "I can keep a secret, can you?" Wink at her when you say this and give a cocky smile.

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Attraction is not a choice.

I think we need more details in order to give you any real material here.

If you have never spoken to her before, that line would be kind of bad to open with, imo. Why? Since I think it says: "Hey, you're so popular, I can see that, but I think you're a slut. So; how many boyfriends do you currently have?"
On the other hand, if you do have spoken to her before, there is no need to open her like that, then you could use that line later on in the conversation if you feel like it. But I do have to agree with AlGreen, don't speak about boyfriends, unless you don't want her.

Assuming the two of you haven't spoken, I recommend you to open her like any other girl. You CAN NOT treat her like she is popular.

Dam she must be good at game lol.

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Now looking back at all we've had...
we let so many dreams just slip through our hands...
Why must we wait so long before we see
How sad the answers to those questions can be?

I think what you should try to do is get yourself into the convo. Dont try to come in with a corny line just get yourself into the convo. Then while your in, make yourself known to the group and work your way from there.