I didn't care for Gwen either, and her obsession with trying to figure out why Dawson and Joey broke up and why their not together now was really silly and immature to me. The only thing I did understand was after she saw Pacey and Joey kiss, she said it would of been bad if Dawson saw that and that they need to tell him. I personally understood that, but yeah what I don't understand is after saying that and seeing that Pacey and Joey have feelings for each other (and when I rewatched the episodes last year when Pacey says hey to Joey and they share that look before she walks away in the kitchen, Gwen noticed it so I think she suspected something. Oh and before that when Dawson and Joey were explaining why they didn't work out and Joey said "Then he asked Pacey to look out for me" and she said "What does Pacey have to do with this?" I wonder if she suspected something then too) she pushes Dawson to be with Joey and get her back. WTF?
That just makes the situation more messy so in general I don't get her idiotic actions.