Who do you think Jill would expect Bella to call? As you've said in the past, Bella doesn't seem to have a lively social circle at the moment.
Only because we haven't seen anyone beyond Jill and the MC, and possibly even Cathy, but it doesn't mean there aren't some other people. Jill could be just as confused as the rest of us as to who else Bella has to call and just trusts that Bella is calling someone she knows who isn't the MC and who might be available.
Also, Jill DID have a problem in the library. She had to be talked into staying by Josy, then roped into D&G by Magnar. On top of that, she probably would have left with Tybalt if not for Sally. Jill knows full well she's "supposed" to spend time with Tybalt and not with the MC.
And that's the point. She gets talked into these because she's a people pleaser who doesn't want to let people down, which is why she'd allow the MC to be there if it's what Bella wants and is also why she's so torn about about this situation (the blackmail) because it's one where she feels she can't please both parties.
And before you say "Bella will be just like Sally," keep in mind that in that case Tybalt decided to leave rather than continue to press Jill to toe the line. If he leaves, no doubles. If he stays, Jill will have to either call Tybalt's bluff on her own or knuckle under. Those are the two scenarios I just laid out.
But Tybalt won't leave and Bella wouldn't make him like Sally did because here he'd likely be stuck between a rock and a hard place too. He wants to woo Jill and spending time with her is how he hopes to do that, but he also knows Bella is a key influence on Jill and befriending her could help him win over Jill. But, if Bella threatens to leave because Tybalt is against the MC joining, that would upset Jill and he wouldn't want to do that, so in order to continue his efforts to keep Bella on-side and to keep Jill happy, he'd have to let the MC stay.
So Tybalt can't leave otherwise he gives up time with Jill, and he also can't let Bella leave as this doesn't help his ultimate goal. Tybalt may also see this as a chance to show up the MC and impress Jill by being better than him. If Jill were to question Tybalt about it later, his reason is simple which is that he did it out of respect for Bella and because Bella is important to Jill. It's an easy excuse that lets him justify breaking his own terms whilst also making it seem like he it did for a selfless reason.
It stopped being a joke in Episode 6 when Jill bought into his ultimatum! If Tybalt remains the one-note buffoon, then Jill really is the sheltered fool people often accuse her of being. That's worse than Tybalt being a viable threat, at least in my book.
We all know Jill is very sheltered and naive, but this also falls into another archetype, even if they aren't always as naive and innocent as Jill.
These kinds of character dynamics in a love triangle, where the woman is either wittingly or unwittingly naive to the faults of their current partner/pursuer whilst the new guy bests him at almost every turn and/or proves himself the better man, are all too common in fiction and I see no problem with it also being employed here. One such example is Wedding Crashers, where Bradley Cooper's character is the rich, arrogant douche who Rachel MacAdams continues to like and defend even when Owen Wilson is showing himself to be the better man.
If this is the moment when Jill calls his bluff and humiliates him yet again, fine by me; I never liked that plotline to begin with. But in that I case I expect a real relationship with Jill (or fireworks if he's been sleeping around), because there's nothing left to stand in the way. I'm sure as hell not going to play along when the MC tries to climb onto Jill's balcony at night because "we can't be seen together."
Not a fan of Romeo and Juliet, I take it?
Oh, and on an unrelated note, am I the only one who was rooting for Wile E. Coyote because I got tired of watching the Road Runner humiliate him?
Yes.