If your (or your wife's) fresh water diving is mostly wrecks, there really isn't such a thing as "too bright." (If the water is turbid, though, consider a bright light with a narrower beam spread.) However, if you are mostly interested in fish and such, then as others have said, even inexpensive ($50-70) lights can be too bright--the critters don't like it. The DGX 600, a house-branded light from Dive Gear Express, is already slightly brighter (rated at 600 lumens) than I'd like when doing a coral reef night dive. My wife and I each have two DGX 600s. There is also a brighter (rated at 800 lumens) DGX 800, as someone mentioned above. The same lights are sold under other brand names, by the way--they all come from the same factory in China. That's also true of other dive lights in this price range.
Consider getting two identical lights, which is quite practical in the price range I mentioned. The one is in the diver's hand is the "primary," and the one in the diver's pocket (or otherwise stowed away) is the "backup." Even the inexpensive lights are pretty reliable, but if one happens to fail on a dive, switching to the identical backup will feel seamless. Another advantage of the inexpensive lights is that if you lose or break it, you can just replace it without breaking the bank, too.