At what point did Margot go from fearing Toby to being romantically interested in him?

Probably somewhere in her early/tweens where she initially would have been aging out of Toby (The time where most monster's kids would be auto-retired from the system and have their file shredded.) I don't have the specifics down but an event would take place where young Margot was not at home, perhaps on a school camping trip or out at a grandparents house in the countryside or some such. If Toby is assigned to her that night, whatever route he uses to enter the human world will guide him to Margot so he can follow to scare her wherever she might go (some monsters may choose to not scare their kid if they are out of their home in order to have that certain breed of fear that stems from returning to the one place your supposed to be safe. Toby is a Stalker style monster though.)

Event A during that time happens and Margot is very down. Maybe her parents are going through a divorce, a beloved and close relative dies, or maybe she's getting bullied at school. Toby arrives to scare her, intending to make it a big memorable scare because he knows Margot is getting on in age to stop believing in monsters so it could be her last scare, especially with Event A giving her REAL things to worry about. Event C then happens which is either Toby's scare goes completely wrong which puts Margot in some kind of Danger, OR Toby arrives for the scare and something else puts Margot in some sort of danger. Event D is Toby saves her from whatever danger she's in but takes some kind of major damage for it, getting Margot back to where she's supposed to be and slinking back under the bed to lick his wounds.

On Toby's side, the injury takes him out of work for a few weeks while he recovers.
On Margot's side, the monster that tormented her childhood just saved her, getting really badly hurt and now hasn't been seen for a few weeks. The fact that from her perspective he could very well be dead and she may never see him again triggers a fear in her that glitches her file and keeps it open (Something that is foreshadowed in the pitch pilot as the first good scare he's gotten out of her in years is his yelling that he's going to turn in the paperwork to get reassigned and Margot's file rightfully closed).

By the time he's returned to work again Margot is able to express that she was scared she'd never see him again. Toby should have reported to his job that she was no longer afraid of him and as such the file needs to be closed manually, but he doesn't as although he would not admit it he enjoys the positive attention while being simultaneously exasperated by it. After this Margot immediately starts acting like a tween with a crush (Because that's where she's at yo) and once again Toby does not report it, initially claiming it's because he doesn't want the inciting event looked into further in fear of being reprimanded but as time goes on "How long have you known she's not afraid of you Tobias?" can be added to the list while Margot's affections evolve from innocent crush on her savior/personal monster that is hers alone (He actually has other assignments, not just her) to growing up with her until them hormones hit hard and she's planning their future together... which then evolves into the constant harassment while his mouth says no, but his bio-luminescence and... not reporting the file... is saying yes.