I think family all mean well and it's difficult to get away from the traditional family treats on special days. For us, we always have eggs benedict, and I just had to go with it today. But, that's it....I had a small breakfast with Greek yogurt and a banana, then the eggs benedict, and a snack. Supper is already planned with my menu in mind, so it's good.
I think that it's ok to indulge a little, especially if you watch your portions, add lots of veggies to your meal, drink lots of water and try to get out for a walk or something fun with the kids & family.
PS> I think it's wonderful that your mother-in-law was so thoughtful - she did try to lean out the fat a little with chicken sausage