Her Hero Spat Roller is in the room and the starting panel is a reference to a sunken scroll.
I looked back on the comic. Callie has a Pokemon Red game from the Pokemon Red vs Pokemon Blue Splatfest. Her room has Zombies on the walls from the Zombie vs Ghost Splatfest. There was some trash in her room from the Messy vs Tidy Splatfest. And someone already mentioned Pearl and Marina announcing the Cake vs Ice cream Splatfest.
Nice work. There are a few more references in her room but you did good to notice all those.
I'll find them when I get to them =w=