A grandmother of one's spouse.
My grandmother-in-law is a good person.
The great-grandmother of one's spouse.
My great-grandmother-in-law is a good person.
The great-great-grandmother of one's spouse.
My great-great-grandmother-in-law is a good person.
Spouse's great-great-great-grandmother.
My great-great-great-grandmother-in-law is a good person.
Spouse's step-great-grandmother.
step-great-grandmother-in-law.