I'm pretty sure that she doesn't know that Ichika is an alien (at this point), but she certainly knows something is off. Will she know by the end of the season? Absolutely. Remon herself is definitely not an alien. She's just a bored Queen-type character. Think of Kanade in Mayo Chiki, Mitsune in Love Hina, or Mikako in Sora no Otoshimono.

Ichika made herself a target of that type from the first moment she appeared.

Remon seems to have the reputation that she's already messed with all the third years in the school, and all the second years too. The only fun she has left are first years and transfer students. Other students are afraid of her, they're not ignoring her because she's weird, unsociable, or shy. They initially protested her taking/monopolizing Ichika, in a tone that implied Ichika should be beneath her gaze and left alone since Ichika is their classmate too. Remon insisted, they relented.