According to wikipedia:
certain types of "brick tea", made from old leaves and stems, have the highest levels, enough to pose a health risk if much tea is drunk, which has been attributed to high levels of fluoride in soils, acidic soils, and long brewing.
I'll bet you can guess what the Lipton or whatever cheap teabags she was using had in them. Quite likely said "brick tea".
I don't drink "brick tea", but I do keep it on a boil, in order to achieve the highest phenolic content.
I have prescription toothpaste. I'll have to check if it's that kind. It does work amazingly well at staving off sensitivity.