Heating and cooling issues aside...it sounds like you might also want to concentrate on what her real needs are. It doesn't sound like she requires anything more than a small, efficient 4-cylinder 'commuter' car rather than saddling her with a V6 or V8 highway cruiser like a LeSabre or Lucerne. With her short trips, it sounds like she'll rarely get up to operating temps no matter what she's driving, so buy her something inexpensive, yet reliable and save the leftover for a muffler fund....she'll likely be going thru quite a few of those if her exaust temps never reach optimum. I recommend something with a timing chain versus timing belt if she plans to keep it long term. My neighbor's Acura TL is experiencing climate control problems, so I recommend shying away from those as well..she's getting ready to drop >$1000 to get that replaced. Keep it simple for Granny...efficient, cheap maintenance and easy to get in / out of parking spaces. Oil changes won't be happening very often, so IMO it's not worth worrying about that small expense.