Complex sentence: This was probably in large measure because she exercised power more directly, acting as regent for her mentally incompetent son as his mental condition unimproved and was a puppet controlled by her and her son-in-law, the grand vizier Kara Davud Pasha.
Split into simpler sentences: This was probably in large measure because she exercised power more directly, acting as regent for her mentally incompetent son. Mustafa's mental condition unimproved and was a puppet controlled by her and her son-in-law, the grand vizier Kara Davud Pasha.