Sounds like your wife would really like the Old Port area in Portland. I'm not good with adding links, but if you google "Old Port in Portland" I bet you'll find helpful info on the area. The Old Port is loaded with small, one-of-a-kind type of shops. It's located near the waterfront. The area also has a lot of non-commercial/chain restaurants. Some of the walking is uphill, depending on where you park, and most of the streets and sidewalks are cobblestone, so I suggest comfortable footwear.
If you're interested in a beach that is only twenty minutes south of Portland, I highly recommend Old Orchard Beach. It is probably one of the widest strands of beaches in Southern Maine. There are a lot of not too expensive motels that line the beach area from about a mile or so on either side of the main street. There is a small amusement park, arcade and plenty of eating stands at the bottom of the main street.
The beach can get quite crowded around the pier area in the summer, but the further you head away from the main street, the less crowded the beach gets. In one direction you have Pine Point and in the other direction there is Ocean Park. Both are smaller, quieter areas, but are also on the gorgeous seven mile stretch of beach.