This is actually pretty common and she won't remember anything about the episode b/c she was sleeping! The best thing you can do is walk her back to sleep and take precautions to make sure she is safe, just in case.
-put a bell on her door so that you wake-up if he leaves her room
-keep ALL exterior doors locked at night (bolt-locked to be certain)
-keep stairs blocked off
Help her unwind before going to bed- have quiet time so that her brain slows down before going to sleep. Kids outgrow this in time, but it's scary while it's happening. My husband walked in his sleep until he was about 10 and then it just stopped.