There's no way a young girl would have worn pants, especially one from Chicago (where social pressure and fashion are more staid and strict).
Gigi Perreau's character is referred to as "Vickie" on screen but "Carrie" in the credits.
When Simon Battle and Lucas are working on the patient, two bad guys bust in to kill the patient. Lucas knocks the gun out of the bad guy's hand and keeps his rifle on them. However, the hammer is down on Lucas' rifle, making it unready to fire. The Rifleman would never make this mistake.