There are religious anti-demon private schools. One reincarnation of Mabel is sent to such a school. Either Dipper doesn’t notice because he only caught that Mabel was reborn, or he does notice, but can’t help because they have good wards, R!Mabel will be punished for being with a demon, and he’s scared of the prejudice she’ll show toward him from her learnings. To make matters worse, she has a passion for art that the school doesn’t appreciate because she subconsciously incorporates Alcor imagery and other supernatural elements into her works (even unicorns are frowned upon). When they do meet, however, he is saving her and several classmates from being sacrificed. The sacrifice was either organized by the school in an attempt to eliminate Alcor (though this is more unlikely than ironic because what is the point of risking the lives or your pupils to destroy the thing you hate?) or was by an outsider the group looked up to. R!Mabel is more ticked off about this than scared of Alcor. Meanwhile, Alcor is awkwardly trying to make sure she’s okay while still worrying about finally having the confrontation.
“Are you okay? Do you want me to leave, or..”
“Poop! I actually gave up drawing for this?!”
“Look, I just hate human sacrifices. Don’t hurt anyone over being saved by a demon.” Alcor looks back at the circle and twiddles his thumbs nervously. R!Mabel turns to Alcor, pausing in her rant.
After tilting her head in confusion, she laughs, “Y’know, for a demon, you’re kind of a dork.”Alcor freezes and gapes at the girl.
“Hey, could you give us directions, or are you going to lead us to some underworld to eat our souls?”
“Do you want me to take you home?”
“Sure! You guys wanna come with?” The other group members shake their heads in horrified objection. Shrugging, R!Mabel takes Alcor’s offered hand. With a blink of an eye, Alcor blips them to the dorm’s front doors.
“Oh ho ho,” R!Mabel laughs, “Mother Robinson would FLIP if she knew what just happened!”
After that, R!Mabel starts rebelling against her teachers, summoning Alcor just to hang out, and drawing everywhere. After ripping up the drawing she was making of a certain well-dressed gentleman with butwings, her teacher finds herself calling a custodian to clean a replica of the drawing off a spot of the ceiling that the girl shouldn’t be able to reach. I might use her in a future story, so let’s just say her name is Marceline, or Marcy for short.