The Girl on a Broomstick (1972)

Saxana has the enthusiasm, but lacks the right talent to become a witch. So she's kept in for 300 years - nothing unusual for a sorceress' school. Being bored, she skims through the magicians' lexicon and finds a formula which brings her into the world of the humans for 48 hours. There she meets the friendly Peter who takes her with him to school... and the adventures begin.