Serious question--did I miss a past episode where Debbie verbally "poisoned" Cousin Coltie about Larissa? Mea Culpa if that's the case, because...
I am having difficulty with some of the talk about Debbie, because I do see a lot of it as supposition, i.e. "she must have been violent before to inspire Larissa to threaten to call the police so easily." Keep in mind, in the same scene, we witnessed Larissa's irrationality of Debbie's (non) slamming of the door. The door didn't get unhinged, but Larissa certainly did.
And as far as Debbie having a smirk on her face during the rage-fest between Larissa and Cousin Coltie, I thought she acted as the only adult in the room, engaging and distracting the young children.
Regarding their financial issues, Larissa apparently has never heard of the concept of budgets. She reminds me of Veruca Salt from Willie Wonka who just would just stomp her feet and demand, "I don't care, I want it NOW!"
Coltie is at fault for putting Debbie in the position of credit card gatekeeper with Larissa. Instead of Larissa blaming Coltie and his budget, she takes her frustrations out at Debbie. Larissa can't risk blaming her green-card giver, so she pivots to Debbie with everything, to the extent where she has to manufacture faults.
And by the way, I am getting uncomfortable with the remarks about Debbie's appearance which are simply age-related. But I do agree she actually would probably be happier in a retirement community of some sorts.
Bottom line, I mainly hold Coltie at fault here. Boy's in no position to take on a wife. He was plenty happy living with his mama, his living room slot machine and his sparkling cat wardrobe. Sadly he just had some certain needs (shudder) that were going unmet, and in trying to fix that, he's screwing up other lives.