Am I a Jew if my mother's mother's mother's mother's mother was a Jew? Even if along the line one of my foremothers converted to another faith? I'd just like a better understanding of matrilineal descent in Judaism.
You would still be a Jew. The lineage of a Jew never breaks, regardless of a person's apparent conversion to another religion. The lineage is through one's mother and that is unbreakable. There exists no such thing as conversion from Judaism according to Jewish law.
See the Gemoro (Sanhedrin 44a):