As I understand it, the strict definition of Jewish descent is purely. You have to go back around 100-200k years to reach the most recent common matrilineal ancestor, and I'm reasonably confident she was not Jewish.
100-200k years? Based on... what? Judaism's earliest trace lies at about 1500BC... so not even close to 100k years.
How many ancestors you have it just a function of how many generations you look back, and with each successive generations it doubles. At some point in the past, the entire world is your ancestor.