Complex sentence: Gloria Reuben's addition into the main cast opening credits was in the 6th episode of the 2nd season her removal from the credits was in the 7th episode of the 6th season.
Split into simpler sentences: Gloria Reuben's addition into the main cast opening credits was in the 6th episode of the 2nd season. Her removal from the credits was in the 7th episode of the 6th season.