Yeah, I doubt the one-time-only megadose theory. While it's definitely possible that there was one main incident that sent her to the hospital, "the family medical emergency", it sounds like having that much still in her system months later from ONE incident would have killed her. No, I think she got into it more than one time.
Also, just wanted to correct a mistake of my own from earlier: I had, like many, conflated "worst day ever" with "family medical emergency". It sounds like "worst day ever" was a while back and before the heavy coke arc started, while "family medical emergency" was earlier this year. I know that's been pointed out already a couple times in the Rackets threads, but I still see people conflating the two events.
And I don't even assume that was an overdose. A guy with five kids, a wife and two lovers in his Quoverfull, older parents and in-laws, plus other Kayla relatives nearby, has a lot of possibilities for "medical emergencies". But, yeah, an overdose is certainly not out of the realm of possibility.