In a mix/ girls group setting, how would you identify the girl who are the most interested in you?

After asking a girl out within a group, and she said she has a bf. Would you still go for the next girl who heard what she said?

I usually have a target before approaching the group, and after chatting up with everyone, and get a feel if that particular girl is interested in you. However, other girls might show higher interest into me, and I get confused of who to pick. When girl A in the group rejects you in front of her crew, is it a big nono to go for girl B for the number? It seems to degrade the girl B so much, like a second class meat.

Cheers