The exact same thing happened to me several years ago. Crawl under the trailer and look at the gear at the rear end of the slide or the end that will not go in. The set screw holding the whole shaft or the gear itself has most likely loosened up and allowed the shaft or gear to move out of the mateing gear. I called a RV tech out to the campgound and about 30 seconds and $75 later he had it fixed. I suspect the same thing has happened to yours as the symtoms sound exactly the same. You may have to have your wife slowly operate the button to rotate the shaft so you can see the setscrew.
By the way, it is possible to push the slide back in. Have someone inside operate the motor while you and a couple of others push on the outside. It will go in quite easily once you get past the initial "hump" where the slide is going uphill on the little indent well at the edge of the trailer. I had to do this as it happened to me on an overnight stop on our way to Florida. Left it in until we got there. Finally got it fixed after we reached our destination.
Barney