Could you maybe do both? The schools I applied to asked for 3, so maybe an OT, an undergrad professor and your CNA teacher? If you don’t want to ask an undergrad professor, then the CNA teacher alone would probably be fine too.
I was nervous to ask professors from Undergrad because it had been over 3 years since I graduated. Once I asked though, I had three professors respond that they’d be happy to! I was really surprised — I was a good student, but I wasn’t overly talkative in class or particularly close to my professors. 🙂