Is there a reason why she cannot bike to work her four miles? I don't know the area or the bikeability or walkability. That would help decrease miles on your car, or let you eliminate a car, that will save money. If you move between the two places, you have to drive.
I've been thinking about this a lot lately. Job stability being what it is these days. We bought our house 9 years ago and picked the location because it was between our two jobs, which were about 13 miles apart. I had a 12 mile bike ride to work and my husband had a 5 mile bike ride. So he rode 3x a week and I rode 1-2x a week. Then my husband changed jobs 6 years ago (previous company went out of business). Long story short, we work 1 block from each other, 10 miles from home. Boy I wish we lived in Goleta. We wouldn't have to drive as much.
But housing markets mean it's not advantageous to sell and move.
You should consider the cost of commuting when you do the math. For example, on a bike ride yesterday I was thinking about it. We just started biking to work 1 day a week. That saves 20 miles of driving. (I bike to work, hubby bikes home). If I buy a new car at $20,000, and I drive the car 100,000 miles before replacing it, then it's $1 for every 5 miles of driving. This does not count gas, maintenance, insurance, etc. only the cost of the vehicle (most mustachians do better than this, but this made my math easy while biking.)
So each day of driving to work is $4 for cost of car alone and $3 for gas. $7 a day to drive (plus maintenance).