And I just watched back the interactions with Bella in Ep1.. I know you can't really based an argument on this since it was the beginning and DPC was fleshing out his characters, but... She's the Ice Queen, she's checked out, seem uninterested, when she catch you naked, she's just angry and judgmental... And the moment you tell that you lost your mother at birth, she completely changed... So it might've been the moment her plans shifted (or she pushed them further a little bit). She didn't have the same urge that night. The day after, she saw Jill and MC talk, so she went into "Protect Jill" mode and wanted to make sure he wasn't the kind of boy who would take advantage of the situation with a vulnerable Jill (which fit with the diner she wanted to have with MC). Then she started being more and more happy, making more friends and being a teacher (which I don't remember if it was her goal when she was a librarian or if she became a teacher just because they were short staff).
I kinda hope I'm not cooking.....