If I were you I would surely get rid of her asap.
I think consoling your kid if he feels bad is better than actually keeping some kind of a psychopath (if at all).
I also like the idea of putting cams to keep an eye. But don't think its a cost effective long term solution.
Trust is something very essential with your maid as she has a lot of control over a lot of things (like what food you eat) irrespective of your vigilance.
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