Having worked in police cells, I know the difference between necessary control and restraint, and unprovoked, unnecessary behaviour. This definitely seems like the latter.
But, we only see what the CCTV shows us, and I'm sure there is another side to that story. If a custodian is showing violent/threatening behaviour, than a control and restraint situation is absolutely necessary. If she was suicidal, again, necessary to remove anything that she can use to cause self harm. We don't see the timer on the video; this scene could have been going on for hours. If the girl is not going to give, then action needs to be taken.
I feel for her, her dignity has been taken away, and she wasn't treated great. But we don't know what her behaviour was like prior to that.