I don't see how suggesting a person sounds like she has candy in her mouth is disrespectful. That's exactly how she sounded. It's a specific, concrete criticism. (And it's pretty similar to sounding drunk.) I also agreed with the comment that "she also does [the] very stranges[t] things in terms of [speeding] up and concatenating syllables."
ETA: Moderators, maybe this would be worth making its own discussion?
My two cents:
Saying it sounded like the narrator sounded like they had candy in their mouth or were drunk gives the impression, to me, that the person saying this does not think the narrator took their work seriously enough to apply themselves to it properly. In most likelihood, when you can't understand a narrator it's probably either a technical thing (bad microphone, echoey recording environment, bad software) or it is just the way the narrator's voice sounds.
If it's just the way the person's voice sounds, then, well, there's a high probability that anything you don't like about the voice is not within the narrator's direct control--a person's voice is part of who they are that they carry around all the time, so is a little more prone to becoming a personal insult than criticizing aspects of a story. And, since narrators have historically worked on a volunteer basis (I don't remember if that's still true) if the first forum comment from a listener is a personal insult that not only may discourage this specific narrator from returning, but could discourage any other potential narrator from throwing their hat in the ring because they're worried that people will mock their voices.
One can say "This ending was totally unsatisfying" without insulting the author because the ending is not part of the author it is a product of the author, but since the narrator gets to use their own bodies to send some sonic waves to be coded into 1's and 0's in some kind of discernible pattern, there is a more immediate physical involvement there than the author. But, let's say the narrator sounded like Gilbert Godfrey--maybe it's TRUE to say that they sounded like that, but since Godfrey is generally known for having a comically grating voice, I'd say it's rude to say that in episode feedback (obviously that's not what you said, but that is an example).
One could simply say "I couldn't understand the narrator clearly, so I stopped listening" without making it sound like one thought they were drunk or eating at the time of the recording. This can still be useful feedback--if enough people had trouble understanding, then this is important information for the audio producer.