Church choirs can be anything from lousy to excellent but most of them are pretty decent. They are usually full of members aged 65+ so, while only the smaller ones might be willing to add another one of this age group, any female in her forties would improve the average age and should be very welcome.
Apart from the North German Radio Choir, the State Opera Chorus and maybe the Choir of St Michaelis ("the Michel" which has the best church music in Hamburg),* I would not expect any choir in Hamburg to exclude a 40+ female singer as an applicant per definition.
The Symphonic Choir Hamburg does not write anything about applicaton but gives contacts per voice group. Their choir director Matthias Janz is truly excellent; we attended many of his concerts when we lived in Flensburg A.D. 1988-90, and even one in Budapest later.
Good luck to your colleague, and tell her to learn to say Hummel Hummel!
* Not even the Michel's choir mentions an age line! - And all the five Hauptkirchen can be expected to have very good church music indeed.(i.e. the Michel, St Petri, St Jacobi, my own St Nicolai and the most beautiful St Katharinen)