Comfort bikes were conceived for rolling around the neighborhood and general getting exercise and fresh air, so I think you'd do fine. Comfort bikes, based on a mountain bike, offer a low center of gravity, enough tire air volume to handle sidewalk transitions, poor or loose surface roads, and an upright riding position for good visibility and less stress on the wrists and neck.
Take the time to test ride to get the proper size. Wear comfortable clothing and suitable shoes while shopping. Most have adjustable stems, etc... for fine tuning the fit, but you need the right size frame to start. Comfort bike frame sizes are often expressed as S-M-L-XL or 15-17-19-22 inches. If the rider is near the edge of two sizes, be sure to test ride before buying a different brand, as there may be minor size differences from brand to brand, even though both may be a "17".
If you pick a price point, say $350, the bikes themselves won't differ all that much between brands. Quality and components will be comparable. One important difference can be the shifters, some bikes have "Rapidfire-style" (thumb and forefinger) shifters, others use rotary "Grip" (like a motorcycle throttle) shifts. Either will work well, but some folks develop a preference after trying both types.
Buy from a shop that treats you well and makes you comfortable, offers free adjustments, etc... vs. sticking to one particular brand. There isn't a huge profit on these bikes, so expect shops to compete via a higher service level vs. price markdowns. In the comfort bike realm, (in no particular order) Trek, Raleigh, Giant, and Schwinn, all make excellent bikes.
Once you get her one, the best thing you can do to keep it riding well is proper tire inflation. Bicycle tires can lose air surprisingly quickly, but still look inflated. On a comfort bike, a tire with 65 psi will ride much differently (better!) than 45 psi, while looking similar to the eye.