lol Saratoga's face between Shinano and Illustrious ~

...

Wait a second! I see 10 characters and 9 characters tags! someone is missing O_O

Edit:
Gelbooru, Danbooru and Konachan have also the Cheshire character tag, but I can't recognize her...?

Source post have several character tags, but not Cheshire

Edit #2
There's a comment in the source post that asks "who is the falling girl? lol " but has no replies

Another one asks "那个滑倒的大莱莱是谁啊？"(Who is that slipped Diners?)
This one got a reply:
郡，放大可以看到猫耳朵 (County, zoom in to see cat ears)

I guess the cat ears and the short blue hair made other booru guess she is Cheshire? I can't really tell if those are cat ears or hair ribbons tho :V it's barely visible...

Another comment asks "那个滑倒的是谁啊" (Who is that slipping?)
This one too got a reply "根据发色可能是天狼星" (May be Sirius depending on hair color)

This is a very serious internet mystery I'm not gonna catch sleep tonight if I don't solve it @.@

I see Club3 doesn't produce hi-res artwork to Yandere's standards, so got an artist entry for him with his URLs included. https://yande.re/wiki/show?title=club3

I also tried to solve the mystery but could not figure out who she was.
I think she has shorter blue hair than Formidable or Illustrious, which is a clue.
I feel Chapayev is the most likely.

@Genex
Thanks for adding the artist info!