I'm not sure how comparable the room prices are, but you could see if your MIL's company would allow her to book at a nearby hotel, even though it's not the one the conference is at. You could conceivably book next door at the Yacht & Beach or Boardwalk, get the Free Dining, and pay close to the same price as the Swolphin. (Though if the conference requires her to stay at the Swolphin, I guess she's out of luck)
I had a friend who had a similar situation. He had a business trip to London, and his company was paying for 2 extra nights for his trouble of flying there for only a day or two of business. After doing some calculations and finding that it was a comparable price, they agreed to pay for two nights at Disneyland Paris (with tickets) instead of London. He just had to pay to get himself there and back. (Which turned out to not be the cheapest thing in the world...)
-Rob