How do I file probate for my deceased wife to collect her inheritance from her deceased mother's estate?

You need to file with the Probate Court in the County in which she lived just before her death. See a good local lawyer if you need help. Good Luck.

Probate needs to be filed for your mother-in-law's estate.  If she has relatives or a spouse surviving her, mostly llikely they will file and be appointed personal representative of her estate.  But you can apply if they do not or if she has no living relatives.  Her estate will be distributed in accordance with her Will or, if she doesn't have a Will, in accordance with the laws of intestacy.  I don't know if that means that your late wife's estate is entiled to an inheritance but it all happens through the probate process and by the actions of a court-appointed personal representative.