As much as I love to see polyamory in yuri, it certainly seems weak here...but I'm also wondering if, rather than polyamory, the author wrote this as an opportunity for Mei to learn what each arrow type means. She's already seen that arrows come in all kinds of shapes, sizes, quantities and intensities, but she has yet to actually figure out what each individual arrow really stands for.
While a part of me wants to see poly here, it makes more reasonable sense for Mei to use this opportunity to find out just what each arrow type stands for. And if she ends up playing cupid for her friends...well, it works.
Frankly, I'll be laughing my ass off if she ends up falling for the Student Council president. But hey, at this point we really don't know enough yet. So, we can only wait and see.