You basically repeated what I said and then added some information that might mislead her into believing the Cathedral has access to marriage records other than its own.
The Metro Archives has marriage records, including bonds and registers, up to 1916, including transcripts of the registers. That would be the preferred place to get the information if Sheila lives near Louisville. Otherwise, if she lives further away, the Filson is going to have records on microfilm, which one would have to pay to be searched, and which could instead be gotten on loan to a Family History Center for $7.50 at current rates for a 2 month loan.
Re the Cathedral, it is a parish in its own right and maintains its own parish records. Other than that, individual parishes maintain their own records, or if they have been closed, those records reside in the archives at the *Chancery*, which is not part of, nor located nearby, the Cathedral.
Now perhaps the Cathedral office was nice enough to obtain the record for you from the Chancery, but more often they are just going to refer you to the Chancery which should thus just be contacted directly.