I live in D.C. area (20 yrs) and have my office in D.C. What sights are you interested in? The WHite House, Capitol, Monuments, and Mall area? If so, try the JW Marriott for reasonable rates and great location, right on PA Ave. It is a large full service hotel. I frequently book business people who come to see me there. Also, the Willard is a very historic nice hotel around the corner from the JW Marriott. Great locations for a quick trip. Will you be coming into Dulles or National airports?
I respectfully disagree w/the idea of not staying in DC. You only have a short time and don't want to be navigating the metro (subway) w/an elderly mother. From the hotels I mentioned you can easily and inexpensively cab to anywhere you want to go close by, and you will be right in the middle of the best sites for a one day stopover.