The game calls it "Church in the Slums", and when Aeris talks about it in Shinra Bldg. with those capitals too. Other than that it's referred to as an "old church", and Aeris says "This is a church in the Sector 5 slums.". Crisis Core's say on the matter is that the area is called "Sector 5 Slums - Church".
So I would be happy with "Sector 5 Slums Church" or "Church in the Slums", I don't like "Sector 5 Church" though. Even though it's the only church in Sector 5 we see, it also happens to be the only church in Midgar we see, and the rest of the Compilation too. JBed (talk) 06:34, August 16, 2014 (UTC)