RE: Carbamide peroxide
I am not a dentist, but this is what I surmise:
As you all know, there are people who use hydrogen peroxide
or hydrogen peroxide products to clean and whiten teeth.  It acts
as an oxidizing and bleaching agent.  Solutions of hydrogen
peroxide gradually deteriorate and can be stabilzed by the addition
of organic materials, carbamide in this case.
My conclusion is that as long as the mother spits the stuff out
after brushing and does not swallow it (although I am not sure
who would want to do that) all is OK.  Even if she swallowed any
of the stuff, the GIT would "eat" it right up.