All rounder usually means more compromise in IQ for the most part. In other words, the greater the range of the aperture over the focal length of a zoom lens, the greater the diminishing returns of IQ at the closer you get to the extreme focal range of said lens. Gosh I hope that made sense! There is less of this compromise if the lens is a fixed not variable aperture lens. For example, a lens from 100-300mm where 100 is aperture F3.6 and 300 is F6.3 and a 100-300m where 100mm is F4 and retains this value(F4) and all the way through to 300mm. The constant aperture lens will for the most part kill a variable length over the same focal range. Despite all of that, your wife has a well regarded lens for the price so I would be looking for another lens to complement rather than one to replace. In other word, a lens to cover wide angle to around the 70mm mark.
