There have been others in the past that couldn't figure out how their pup was escaping the Xpen. They videotaped the escape and it turned out they were climbing like Spiderman and not jumping. You might want to consider putting screening over the top of the Xpen to prevent her from being able to get out in the future.
If my memory serves me correctly I believe they used some type of wood to make a frame and attached window screen. Worked like a charm.
