CMU website says they only need 1 teacher recommendation.
Do they accept an additional LOR from a teacher\mentor (not a HS teacher)?
There is a spot to add another recommender on the Common App, so I would assume so. It wouldn’t hurt to send admissions an email to find out their perspective though.
@Pri930 I used the “Additional Information” box to paste a digital version of the LOR form my employer wrote. I also sent the physical copy the COO filled out to the CMU admissions office. Use the space they give you wisely : )