If she does not want her electric bill to go up to much (except in Winter): Get a PS3 Slim.
If she does not want to use heat during the winter (and keep her bill down): Get a 360.
As far as games go, I think she would enjoy either console.
The only difference I can think of for her is the blue-ray drive. She might not buy many movies, but does she like to rent (I saw the netflix + streaming part but does she only stream?) If so, I would go with the PS3.
If no, then go the easy way. Have your wife's friend come to your house one day and just hold each controller. Once she has done so, pick the console that has the best controller FOR HER. No reason to get into what is better for what, or any of that mess, if it is better for her go that route.