Gosh, thats horrible. At the end of the day you are paying for those swimming lessons and she is your child. They should be listening to you.
My girls don't have sensory issues but we had HUGE issues with DD2 and swimming lessons. When she first started she was absolutely terrified. She hated the water and cried a lot, then when she was in the water she didn't want the teacher to let her go, and didn't want her face anywhere near the water. And didn't want to DIE which is what she would scream when it was nearly time to jump in.
I have realised just how lucky we were to find a swim school who will listen to us. I had a chat to them about DD2 about how terrified she was and together we worked out the best approach. We swapped her to a younger softly spoken teacher and they even said they had another teacher in mind if we felt she wasn't the right choice. She was told to be gentle with her and absolutely not force her into putting her face in the water. She did encourage her later on once she had her trust but never forced her to do anything she didn't want to do. Jumping in was done while holding her hands and never letting go from the bench in the water at first and slowly over time she worked on getting her to jump from outside the water. Sure, she didn't improve as quick as other kids but she wasn't distressed anymore and that swimming teacher had her trust.
Years later and DD2 is able to swim and isn't too far behind her twin sister but her teacher can see she is a nervous swimmer. But she can make a very strange attempt at diving in and swim the whole 25m pool. But it took years to get to this point. Although we have now discovered that she can't handle swimming lessons with that teacher she first had. They had very small classes this term and wanted to swap her to the class before but she couldn't even handle the thought of it as it was with that teacher and she reverted back to that scared little girl. So, no problem they just kept her in that class which is usually all by herself and no other kids (since most of the kids didn't re-book this term for some reason) and worked around it.