I suspect that if the OP had already booked the non-refundable rate with the property and then had to unexpectedly cancel to deal with his M-I-L, he would get a much different response.

There's a saying about 'if you have to ask, you already know the answer.' If I were the OP, I would go ahead and book the non-refundable rate and then hope I don't have to change it or hope for leniency. But I wouldn't ask FT to validate my decision.....