#1 Put a stinkin latch on the inside of the window. I'll post a link of the ones we use inside our windows. If you can't use this sort of latch then cut a broom handle the diagonal length of the top of the window and put it in there. That way this window can only be opened from the inside.
#2 There is a video, it may not be posted anywhere on the video that's public but there's a video. A new kid saw it and mentioned it. He saw it. So yes, there's a video. Unless it's been uploaded to a computer somewhere then it's on someone's phone
Let everyone know you don't think there's a video and that it's just a rumor. The call the police, for goodness sake's, they violated your daughter and have a video of her stripping down to shower.
If they had a video of her having sex would you treat it differently? If she was being raped? That's what it's like for her, it's like being emotionally raped.
#3 Find out from the police what to do next. If they go and confiscate the phones they may not even find it. If I took this sort of video and wanted to keep it for power I'd move it to a safer place, maybe the hard drive of my computer or something. They get it off the phone. You can still access your computer or other photo programs with your phone and it not actually be on there.
#4 Make sure your daughter is never alone in your home. She must never do home alone time. As long as she is vulnerable they could break in and hurt her or worse.
This is what we put on all our storm windows. It screws down on the metal part just above the bottom window. It works very well.
http://www.amazon.com/High-Security-Sliding-Window-Lock-I...
http://www.amazon.com/Ultra-Hardware-Aluminum-Sliding-Win...