Complex sentence: Frieda remained a full member of the "Peanuts" cast for just 1961 but her last official appearance in the strip was on March 20,1975, although unnamed girls who resemble her would occasionally pop up in later years.
Split into simpler sentences: Frieda remained a full member of the "Peanuts" cast for just over 14 years. Her last official appearance in the strip was on March 20,1975, although unnamed girls who resemble her would occasionally pop up in later years.