I think you're reading a different story or doesn't know how children come to the world. the FL is younger, meaning her father did had other women when her mother was alive. There's no explanation until now why this happened but if there's non, it means her father was a jerk and your post is defending a jerk.
If I'm not wrong it should be something Jet Lee playing in... Kingdom Under Fire or something along. It's quite an old movie but a very good one.