i wonder what this means

I'm guessing it must be some to do with River Song, but the river reference might not be that obvious either.

she was first in Forest of the dead so that may be key to it

The only water in the forest is River. So in the forest, both Amy (POND = water) and River = water. So is Amy real?? if the only water is River?

But Amy isn't in the Forrest Of The Dead, Donna is. Or am I looking at this really wrong