if the mother-in-law cut them up and didnt rip them up, then you're probably in luck. it's a lot easier
the first thing to do is to scan each piece individually, making VERY sure you have them all aligned EXACTLY the same way; you dont want to have to rotate them in your editor. usually, with most scanners, there is a way to keep pieces or pictures totally oriented exactly the same way. sometimes it's one edge of the scanner and sometimes marks along the side, and if i recall correctly, one scanner actually has marks on the glass plate for this.
once you've got the pieces done individually, take the pieces and put them on a piece of paper of a size slightly larger than the original picture. line them up and make sure they're all going to fit correctly and as close as possible to each other without overlapping. once you've done this dry run and things look pretty good, get some of the glue that is a sort of semi-glue. you dont want a glue that is going to permanently tack the pieces down. you want one that is only going to stick them on the paper but be able to take them off the paper again...sort of like the glue post-it notes uses.
glue the images in place all on that paper and scan that.
you now have your image both ways, in pieces and as one piece. the chances are, if things glued down well, that the glued one is going to be all you need. take that image into your graphic editor and simply clone/heal out the small division lines and you shld be good to go.
all of that is based on if the image was cut cleanly. if it was ripped you've got a bigger job ahead of you.
craig