Upvote:0
Don't know if this helps, but here's two quotes.
Let the Church, our Mother, weep for you, and wash away your guilt with her tears; let Christ see you mourning and say, “Blessed are ye that are sad, for ye shall rejoice.” Ambrose Repentance Chapter X
And rightly do I send my son, the deacon Felix, to bear my letter, and, at the same time, to present to you my duty, in my place, and also a memorial on behalf of those who have fled to the Church, the Mother of your Piety, seeking mercy. Letters LXII
Upvote:1
The closest I could find is In Lucam, 2, 7 (p. 28), PL, 15, 1555, where St. Ambrose says she is:
a type (or figure) of the Church
est Ecclesiæ typus
See: Part II. "The Analogy Presented", §2. "Mary, Mother of the Church" of Mary and the Church by Cyril Vollert, S.J., in Juniper B. Carol, O.F.M., Mariology vol. 2.