Look at it this way, we have the choice to make our offices anywhere we want them to be. I'm not aware of any rule requiring we never change them. Two other things to consider is how this relates to your overall year. If you normally drive 10,000 miles in a single year, an extra 200 is only 2%. You also didn't say if you have been taking other assignments closer to her house than your own. Mileage saved there could make the whole thing a wash.
Equal rights for others does not mean fewer rights for you. It's not pie.
"I prefer someone who burns the flag and then wraps themselves up in the Constitution over someone who burns the Constitution and then wraps themselves up in the flag." -Molly Ivins
Never try to teach a pig to sing. It's a waste of your time and it really annoys the pig.