When I asked a therapist for a recommendation letter, she replied this:
Typically we ask students to write their letter, including an experience you had here that stood out and made you shine, specific examples of your dedication/commitment to working with children and becoming an OT, a challenge you may have experienced, and how it was a learning opportunity for you, something you did that was above and beyond what might be expected of a volunteer, etc. These specific examples will help your letter stand out to an admissions team.