@abconline that's my guess too. With all the red flags the author is throwing around, people are bound to suspect it's probably this girl + someone else, but what if the plot twist is they're ALL working together? Not many would see that coming.
Also I realized she can't be the girl who was watching them in the forest, because her heels' colours are different - in the previous chapter, we clearly see they're white, whereas here she's wearing black heels.
Now I'm convinced it's multiple girls probably all those girls in the picture are the culprits probably tsubasa is an acronym and it makes sense that noone saw or knew that person because it's more than one... or I'm probably reading into this too much