Recommendation from institutional email or private? I recently went to a summer program. Now, I’m asking my mentor there for a recommendation for college. The email account she uses for all correspondences related to the program is private (Gmail). The institution she works at is not related to the summer program in any way. Now, the college asks for the letter to be sent through institutional email accounts (letters from private accounts will be subject to further review).

She wouldn’t be sending the letter in her capacity as professor at the college she works at, but rather as mentor in the program, an institution in itself.

So should I ask her to send it through her private or institutional email account?
You seem to have answered your own question. If you don't want the recommendation to be subjected to further review, you should ask her to use her institutional email address. Anyone can set up a Gmail account, whereas there is a level of authenticity implied by an institutional email address. It's not relevant that she isn't sending the letter in her capacity as a professor, since the main purpose of the email address is to authenticate who she is. The college are requesting that letters of recommendation are sent from institutional email addresses since it reduces the amount of extra work required of them and of the recommender.