I agree with Trish - i would continue the lessons, but like someone else said, maybe one-one one.
Both my girls started at 6 months. My eldest, whom is 3.5 years, still attends. We've had a backward step of late - in November she went in my sisters pool, and went underwater ( 3 adults in the pool, me watching on sideline, i cannot believe how fast it happens), anyway, its really effected her. She would scream and cry at her swimming lessons, moving back into the 2 year old class (when she was 3) and having floaties back on (major backward step). She was petrified of the water. Im lucky in that the teacher is well taught and really cares about her students, she offered one-on-one classes with my DD each friday arvo. I took her up on it. Its been 6 weeks now.
We went swimming today and she swam across the pool (side to side) with no floaties, blowing bubbles and kicking her legs.
I cannot tell you how happy it made me - i actually had tears in my eyes. Its so hard seeing them cry and scream out "mummy....mummy, get me out". But honestly, it will reward itself.
Can you take her to a public pool and pop in with her, take her around the pool ? Show her that you can have fun in the water, it doesnt have to relate to tears all the time.

Good luck hun....