Gwen had only planned on passing out the moment she returned from a trip away from the TARDIS for beer (for her and Martha to split) when she also spotted the Weevil. As she felt for the gun hidden in her purse (along with a vial of Weevil spray she kept just in case) she spotted Owen out of the corner of her eye. She shot Owen a look that would prove to him it was her,"Where is our local version of a pain in the tail?" meaning the Weevil.
But if Owen asked why she looked ready to basically pass out she would only cite the Joker, Crane and not being able to reach Rhys.