My tire recommendation would have to be get 4 dedicated snow tires on some cheap steel wheels.
Also, take an afternoon and make sure your gf knows how to drive in winter weather conditions, I live in Canada and my girlfriend and I are both using all seasons currently and have had a couple dumps of snow (including this morning) and if you drive to suite your tires and the conditions you should be ok. Winter tires just make it a lot easier.
You could also put a bit of weight in the back of her 4Runner to keep the rear from getting away on you. might help slightly.
I think chains and studs are a bit overkill for city driving, I understand throwing them on if you're taking a trip through the mountains but if your city even kind of maintains your roads in the winter then there should be no need for studs or chains. Not sure about where you live but here in Calgary we have gravel trucks and plows when it snows.
I thought BFG AT's were decent in the snow.....