I got married in November of 2018 while active-duty military. My SLR is Florida for tax purposes. Must my spouse still file a PA return since she worked in PA?

Yes, she will need to file, but may be able to get all of her taxes refunded.  You picked the right year to get married as tax law is concerned.  Late in December of 2018 a law passed called the Veterans Benefits and Transitions Act of 2018, (click on link for more information), which now allows a miltary spouse to claim as his or her state the same state as the active-duty spouse.  

This is advantageous for you, since your SLR is Florida, which has no income tax.  Prior to 2018, she would have had to establish residency in Florida with you to claim Florida residency through the MSRRA.  However, the Veterans Benefits and Transitions Act of 2018 allows her to elect Florida immediately (including 2018).

I will provide this caveat:  this law is new, so it is a bit uncertain if PA will allow her to claim Florida for the portion of the year before you were married. You might want to check with PA on that detail.  

To attempt to get the withholdings refunded, prepare the PA return with $0 income (there is a checkbox on the PA return that allows you to do so).  Then, mail in the return (do not e-file), and write across the top:  Per the Veterans Benefits and Transistions Act of 2018, I claim Florida as my state of legal residence.  Pennsylvania will honor her state of residence as Florida going forward (and she may use Florida for any jobs she obtains in the future), and she may get her PA tax refunded from this year.