Oh yeah, I forget about artificial flavorings because I avoid them as a general rule, but very true.
If she sticks to minimally processed leaf and herbal teas, she should be perfectly safe.
Mighty Leaf (one of the few bagged teas I will use,) has this explanation on their website:
"None of our blends contain wheat, rye, barley, or oats, so the tea itself is gluten-free. However, our teas may be processed in a facility that also processes gluten products, opening up the risk for cross contamination."
So if she is ultra-sensitive, that would be something to keep in mind if she is looking for teabags or blends.