Do the Northstars still have issues with carbon-choking? I know the early generations of Northstars were infamous with getting carbon buildup, even with regular 80-mph jaunts down the highway.
But I concur with the recommendation a 3800-powered car like the Bonneville, Grand Prix, Century, LeSabre, Intrigue. Used Intrigues around here are running between $1200 and $2000, a few higher prices for really mint cars, but since Olds is defunct, their resale value tanked.
The 3800 Series II has plenty of get-up-and-go for daily driving, and reasonable fuel economy (you can get 30mpg or better on the highway, which is great for a V6). The motors are durable, and the electronic transmissions (when driving patterns are reprogrammed with moderate-gentle driving) gives butter-smooth shifts (usually have to watch the tach to know when they shift).
If she was into Imports, I'd say steer her towards a Camry or Accord. But, that goes against most of my GM DNA. For new-ish-GM models, you really can't go wrong with a 3800 car.