The most important aspect of selecting a bike is fit - obviously The Wife does not fit on large size frames, but a Small or maybe Medium would work ok.
Aside from fit, the main concern for us larger riders is wheel durability, and specifically the rear wheel. Make sure that whatever you buy has a 'freehub' style rear hub because they are much stronger than the old-style 'freewheel' type. It is also a good idea to have the spokes on the wheel retensioned as most bikes come with machine built wheels where insufficiently de-stressed spokes will loosen and result in early failure. A knowledgeable bike shop can do this for you.
IF The Wife is not an avid cyclist then a hybrid bike is likely the best choice. They can be ridden almost anywhere and are generally light and efficient, as well as having an upright riding position that many people find easy to get used to. If you can find a bike with no suspension than that is also a good idea. Suspension, especially lower cost suspension, is of limited value but adds to the weight, complexity, and maintenance requirements. A decent suspension fork costs ~$500, so you seldom find them on bikes under $1k, and even then, they really don't help at all unless riding off road. Wider tires at slightly lower pressure is a better way to make a bike more comfortable.