Fuji doesn't put a size chart on its website, recommending instead that you go to a dealer and be properly fitted. But that doesn't help much when you're buying second-hand.

So I looked at Giant's website to see what it recommends for the Roam (similar to the Traverse). It puts you on the border between S (17") and M (19"). They are not identical bikes, but that at least leads me to think the 19" would be good for you. Of course, as you already know, the best thing will be to go ride it and see how it feels.