A Certain Thermal Reaction Resulted

 Apple Bloom is the top of her chemistry class, and Zecora is usually more than happy to make the room available outside of regular hours. But when AB shows up to lab late, unprepared, and wearing open-toed shoes, Zecora thinks she needs a lesson in respect.

As I pointed out a long time ago in a post on why some characters get a lot more sets than others, I do like playing with the relationships between them. Sure, sometimes it is characters who have never met onscreen or even cannot have met because one doesn't even have an Equestria Girls version, but more often than not it is based on an interaction they have had in the show or at least one that can be extrapolated given who they are. That's why, for example, I had Rarity spanking her intern and then getting spanked in turn (heh) by her landlord who just so happens to be the intern's dad, or Junebug and Twilight dealing with Spike's greed in a more drastic manner, or school counselor Starlight giving some unusual counseling to one of the Young Six. And in this case, playing off of Apple Bloom's interest in potion-making with both Zecora and Twilight that she showed a few times throughout the course of MLP.