Spouse's great-great-great-grandmother.
My great-great-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.
Great-great-great-grandparent's mother.
My great-great-great-great-grandmother is a good person.
Great-great-great-grandparent's mother.
great-great-great-great-grandmother
1- Stepgrandparent's mother.
2- Grandparent's stepmother.
My step-great-grandmother is a good person.