Complex sentence: There is little information available regarding her formative years (up to 8 yrs-old), during a portion of this time her father was deployed overseas fighting in World War II (WWII) while her mother was working.
Split into simpler sentences: There is little information available regarding her formative years (up to 8 years old). During a portion of this time, her father was deployed overseas fighting in World War II while her mother was working.