That doesn't sound right to me. I would look around for another swim school. Also take her in with you a few times as well for fun, outside of swimming lesson and see how that goes.

I used to be "scared to put my head under" as a child and no-one could ever figure out why. The reason was because one time I went under backwards and got that awful "water up the nose" feeling. I thought that happened everytime you put your head under, so I wouldn't do it. It took years to overcome. Just a thought in case that's what happened.