Realistically any of us can only speculate. There have been accounts mentioned on here of the "sufficient" oral dosage at the likes of, say, Dignitas, having to be followed up with a "finishing" injection where there were life signs after a few hours.
Rikamonie survived, and only just, because she was found and treated. That much seems clear given her description of the aftermath. Another few hours unfound, then very likely lights out permanently.
Like with any drug the differing constitutions and health positions of people will determine the efficacy of the drug in question. Rikamonie may be one of those who, if she were at dignitas, would have required that follow up injection.
As said, speculation, but I'm reserving judgement on the "underdosed/bad batch" assumption for C's N. Rikamonie's here (thankfully) because she was found, not because the N wasn't doing its job.