What do you anticipate her to use the scanner for? If you just want it for her to listen to local police (if they don't encrypt) and fire, you probably don't need anything too complex. Someplace like Radio Shack should be able to help you with what you want in the area she lives. Since you're wanting it in a metropolitan area, you may want to be sure that you can fine tune it, as some scanners only allow channels in fixed increments and you may find you need the granularity that you can't get with fixed increments, you also want it to have a certain amount of sensitivity, so that it will reject the (I dont know the right word) sidebands of interference. (You might want to call it bleedover from channels you don't want to listen to). A lot of police departments use trunks - or like a block of frequencies, so if you find that where she lives does that, you may want to look for a scanner that does trunk scanning.
Sounds like you don't expect Mom to do more than listen, so make sure it's easy to turn on, press the channel she wants and easy for you to tune. The Radio Shack guy in her area should be able to help you. (I don't work for Radio Shack, but it's one of the few places that still actually have people who understand what they're selling when it comes to this kind of stuff.)
My husband's cousins all live in PA and everyone seems to have a scanner that sits on a shelf in the kitchen, always on. The name I remember is Bearcat....that's as specific as I can get.....sorry