Great she came home! My 10 lb lazy bum of a rooster who jumps up a series of things at their lowest point to reach a 3 foot perch has been caught clearing the 5 foot wood fence to get to something on the other side. Had a few younger girls fly up onto the roof when spooked, so clearing your 6 foot fence might not be that unusual. Perhaps clip one wings feathers to deter this?
Things that can take a bird without a trace include dogs (typically kill all and leave bodies around), foxes (typically just snatch and run but will come back), and coons, which often but not always leave a trail of feathers to however they got in. A coon will have no problem going over a tall fence and if a city coon... may have no inhibition from coming out mid day to get an easy meal.