Just some thoughts on Isla's rotten tooth. My brother had several teeth removed around 10 years old because of overcrowding so Isla could have overcrowding or a badly aligned molar there. However, it is also possible even if you brush teeth well, to end up with some dirt. I have some of my baby teeth stashed in one of my jewellry drawers, and one of them that was loose in my mouth as a child has decay in it because I wasn't brushing firmly enough for fear of bashing my tooth out with the brush. So Isla could have had a painful badly formed tooth that wasn't receiving enough attention and brushing, so that's why a random tooth just got decay.
The intense amount of sugar is a problem and probably not brushing properly, so I'm not saying they're blameless. But since there's two other kids with a similar diet and no decay (as far as I know) it could have been a specific dental issue with Isla.
I think the stuff she said about dental phobia frankly wasn't really helpful to sufferers though.