Well, the most important PA would be the safety demo. The safety demo is pre recorded on most occasions. If it is read, it is read by the cabin manager. I don't believe for one moment anyone would make it to CM if they were that unintelligible. Crews are also regularly assessed and provided feedback with any safety related concerns being escalated to base management.
All crew go through an English language test as the first part of the assessment, all training and assessment is done in English so anyone would need a good command of the English language to pass the course. I'm struggling to see how she made it to the line if that's the case.
It doesn't make it right, but they don't listen anyway, BA at LAS is an excellent expample of this. The Southwest evacs too.