Yeah, the girls really screwed the pooch on that one. They should have agreed with Debbie to not vote out Julia if Debbie promised to keep Julia in the dark and pass misinformation to the guys.
Also, the fact that they wanted Julia gone simply because she was trying to play both sides...if you know she is playing both sides you can use that to your advantage, and she is not the biggest threat. It's mostly threatening if you aren't aware you can't trust her.
Debbie went home because she was so obsessed with guys vs girls, instead of playing the game.