I know I am chiming in late, but without knowing the brand of products you are using, I would definitely advise against using products processed in facilities that also process wheat. I have met a number of people who have experienced gluten sensitivity symptoms after consuming products labeled "gluten-free" that are not processed in exclusive gluten-free facilities. In your particular situation, I think your best bet is to do what you said and just warn the person of the ingredients used. In the future though, the only way to be sure is to only use products processed in completely gluten-free facilities.
I have also heard (can't attest to the accuracy of this statement) that people who suffer from Celiac Disease who stop consuming gluten eventually become even more sensitive to it. Please take this statement for what it is, which is just something I've heard from other people, but the point I am trying to drive is to better be safe than sorry.
I hope this information helps.