Did we do something wrong here?

My 18 month old is just getting over a 10 day bout with a stomach virus/flu. He has been without a fever since Saturday afternoon, but we thought it better that he stay home from daycare today (Monday) and rest up. Last night we asked my mother in law to watch him today. In the car, after picking her up this morning, my mother in law tells my wife that she "had the chills" last night, but is better now - no doctor, no nothing (she has a history of not taking care of herself, and downplaying pain, etc). My wife gets home, and after talking we think that it is better to send our (normal temp, eating fine, happy) son to daycare, rather than have him stay with potentially ill grandma.

We tell grandma this. I try to thank her for coming over and volunteering, as the situation is kind of awkward, and tell her that I will take her home. Grandma, however, flips out and says among other things that she should have kept her mouth shut about feeling ill.

My question is: Did we do anything wrong? Our initial thinking was that our son could have one more day away from the possible germs of the day care center - but when faced with grandma (our only alternative option) probably carrying something - we though daycare was the better bet. Frankly, we have had issues with grandma before and really did make every effort to be diplomatic to avoid a blow up. But I was not about to put my son at risk of getting sick again simply to avoid insulting my in law. Also, am I wrong to be incensed that she would consider NOT telling us that she was feeling sick before she came over to take care of my son?

If I was on the other end, I may have thought it an overreaction (if I was definately feeling better), but as a parent I think I would have understood.

Thanks.