Most likely because she was scared. Don't know about you but if something happened like that to me I'd be shitting my pants.
Why? If that Plexiglas is under several feet of water, do you realize how much pressure it's under? The force the bear (who's going through water, which is going to slow it down immensely) isn't going to do anything to the Plexiglas. I might jump a little bit, but I wouldn't roll around on the floor crying.