@dark hawk dude! That's a rough situation to be in, your targets friend didn't approve of you and so your target fell in line with her. Maybe this is something about you where she didn't accept you or maybe she was in a mood but either way this is difficult to overcome when you don't know her. Your target owes you nothing and she already broke circle so your bubbles popped.
If you can't win her friends approval there's high odds you've lost your chance.
You can tease and amplify showing how she's socially clueless or being purposefully rude
"Wow she's very friendly" "I bet she's the life of the party" "she's very talkative, I can't get a word in" - this needs to be said early as soon as she ignores the introduction/ignores you and she might warm up - she can also react negatively to this, don't flinch and laugh it off
You can point out she's rude, "you're being very rude, we're having a conversation" if you're feeling it - "run along and play, the grown ups are talking" you've got nothing to lose here.
Last ditch effort is to frame it that you're too busy. "I need to go but you seem cool, we should get drinks sometime" very low odds at this stage but you've tried everything.