Complex sentence: The "Insurgent" being a fully rigged frigate was considered one of the fastest sailing vessels in the world at the time where three weeks earlier she had encountered the "Constellation" but was able to outrun her and escape.
Split into simpler sentences: The "Insurgent", was a fully rigged frigate and considered one of the fastest sailing vessels in the world at the time. Three weeks earlier she had encountered the but was able to outrun her and escape.