I understand what you mean, Jenn.
Your MIL is probably trying to make herself feel less guilty for suggesting that your DH and DD leave you at home alone by saying that you could lay down somewhere or stay at her house if you weren't feeling well.
I still have trouble trying to explain why I cannot be around too much stimulation.....noise, lights, crowds, excitement.
You have an amazing DH! Good for him for standing up for you. Maybe this is what it's going to take for your MIL to understand.
I hope you feel better soon!