I chanced to ask the hydro-therapist how she was progressing - and did my heart sink (no pun intended). I learned that she doesn't float independently on her back anymore unless rings are slipped onto her legs to annoy her. Without them she just lowers her legs until she's standing in the water.
Now I'm considering bringing her to the school pool to practice in the afternoon. The hydro-therapist thought that might help. In any case it would give C. more time enjoying what seems to be her favorite activity, judging by the way her body and face totally relax the second she hits the water.
But I must confess: I've been talking for years about bringing her to the pool myself and haven't yet done it. It's just too daunting.
Maybe the prospect of posting about it here will provide the push I need.