Cooked many days old ground beef

We have a big problem at home now because of this. My crazy mother in law opened an lb of ground beef probably like at least 5 days ago, she stores it in the original open package. She always gives my son (12) from her food but this time I told my husband to tell her not to give him after I read online that it only last 1-2 days raw once open. Now she's really mad at me and complains to my husband about me making my husband mad at me too. What would happen if I let me son eat this meat after she cooks it?