If she signed it, and he signed it, and he just never registered it and got the title sent back in his name, you both go to the DMV and they do the paperwork, in most title states I've dealt with. It's not black magic, you go with him to the DMV, with the money in YOUR pocket, and they either do the deed or they tell him he has to do x or pay x. No big deal other than potentially some wasted time. I've seen this most often in states where the plate stays on the car, people buy them, insure them if they are smart/nice, and drive on the plate/registration till it expires. Saves money, dumb and silly and illegal usually, but it's cheap.
Now, if the title is still in her name, she never signed it, he never signed it, and/or no notary witnessed and stamped it if that is required in your state, that is a problem unless you want to get
creative. Odds are that isn't the case.