I was more than a bit tired last night, it seems.. hehe, didn't read your post properly before answering :p But anyways.. going into her group is EXACTLY what you should have done. If you want to attract, getting the target's friends to like you is often a must with hotter babes.. and even when it isn't, every friend not liking you is a potential cock block.
Going from isolation to a group situation can of course be a bad thing.. but what you failed to realize was that you didn't really HAVE an isolation there. The group kept trying to pull her back. A good isolation is when you first get the group to like you, and THEN isolate the target more or less with everyones APPROVAL. You treated a 3-set like a 1-set.. and if you keep on reading PUA material you'll quickly realize why that doesn't work very well.
Anyways, for a first PUA-sarge I say you did pretty good. just keep on practicing and you'll get better in no time
