I suppose it really depends on where in Calgary her son lives. If he's near an LRT station and the river pathway system, she could get around easily by train and ride her bike as well. If he's out in the middle of one of the newer suburbs, it could be isolating.
At least you get Chinook winds in Calgary, so it's not all long and cold in the winter. Although, the mess they make is sometimes not worth the warming. I haven't really missed them since moving to Saskatoon. Here we get a definite winter, then it all melts in one big rush in the spring.