Mm, does this really belong in the How Is That Even Possible? Pool? I know vampires are weak to running water, but ZUN never said it would kill them, only dampen their power.
And before anyone chimes with, "But Patchouli made it rain so Flandre wouldn't leave Scarlet Devil," remember than Flan was on a violent rampage, yet still had enough presence of mind to talk to Reimu and Marisa before fighting them. She most likely didn't want her power dampened, so she could continue destroying stuff.
Also, Considering that COMMON SENSE dictates that vampires are weak to running water...
But ZUN never said how running water would show in the Scarlet sisters. Which leaves a couple different kind of mythos to choose. One of which is that a vampire is paralized over and in running water which is the most common. Another would just have their powers as a vampire lost until sanctuary is found. Then this actually brings what constitutes as running water. Some depict tht sensitivity to be on the extreme so that just dripping or trickling would be considered. Others would only choose rivers, rain, and the ocean as running water. Then there are those that completely ignore the running part and just say vampires are weak to water. I find the last one is there due to stupidity
I would put her on the How Is That Even Possible? pool if she was swimming while smiling or something more expressive.
The way I see it, she's only in the water closing her eyes, nothing indicates she's unnafected or actually getting weakened/dying slowly.
I would remove since there is no indication of if she is in a river or the lake. Which still goes under which definitve mythos you would actually want to use.