Manuka honey is used in our hospitals as well as the general population because of its high antibacterial properties, among other things.
Here is a link with more detail. It's been tested over and over again in RCTs. BUT it's a medicinal grade, not the stuff you get in the grocery store (usually). It'll be labelled as such. I keep it in my medicine cabinet.
Started Feb 18 2011
"There's a difference between knowing the path, and walking the path" - Morpheus
New zealanders have been using it for many years and there is nothing dangerous about it. Tell your mum to eat up..
Manuka is just tea tree. The tea tree oil from the plant is quite strong but honey from the nectar is a whole different issue.