My MIL is a very finicky person and she likes to keep things in order in her own home. But as soon as she comes over to our place, no matter how clean it is, she manages to find fault! How do I tell her, she needs to STOP, without sounding rude or crazy!

my dear, you are married to an Indian family, so i am sure you know this is a typical MIL mentality. i would say please ignore it if possible. if it gets out of hand and she really gets on your nerves, tell her very sweetly and say you are impressed with her housekeeping skills, so now that she is here, in her own son's house, she should think of it as her own and keep it clean the way she does back at her place.