There is no evidence whatsoever to support that theory.
Yes, I was being snarky; she is dead, therefore we know she died, therefore there is evidence that she died, and drowning is a type of death, therefore there is evidence that she could have drowned.
We have no idea how she died. The coroner could not determine the cause of death. So there is no evidence to support any particular theory of how she died. Traces of what was alleged to be chloroform, a heart-shaped-image on duct tape that nobody took a picture of and couldn’t be found later, a web search report now known to be false.
But they did own a pool, there was testimony about a drowning, and about how the child could get out of the house on her own. So you could also say that there was no evidence that she didn’t drown (meaning the prosecution didn’t have a good refutation of the drowning story).
It’s easy enough to lie, especially if you already killed. We’ll never “know” how the girl died. All we know is that 12 people who heard of a horrific death that shocked the country decided in the end that Casey had not be proven to have murdered her child.
To me, the fact that 911 was not called after Caylee’s “drowning” is ample proof that it never occurred.