Per helpful suggestions in comments on the question, from @Alexander-Woo and @user111388, I described the context within which I worked with the student, and then later left academia, in the first paragraph:
It is with great enthusiasm that I recommend Student for Grad Program
in Research Field, at Your University. Student was an outstanding
contributor to the team that I led as a postdoc at My Former Institution.
Although I have since left academic research to work in industry my
research experience with Student demonstrates her excellent fit and preparation
for a career in Research Field.
And amended my signature (also in the question statement), to clarify I meant my most recent academic institution, at which I worked with the student:
Former Thisorthat Postdoctoral Fellow
My Former Institution