Certified softball maniac
I think it depends on the pitcher and how good her change up is. My DD's TB team has three pitchers. With two of them we throw less than 10% change ups. With one her change up is her best pitch, so she probably throws 30-40%. You call pitches based on your pitchers strengths and the batters weaknesses.
I'm a fan
The last game they let her throw all her pitches and it kept them guessing. They played a 4a school and there a 1a and only lost because of errors. So it works a little better to mix things up.