When did Rosa Z Owens & F W Kosack marry???

I have very limited information on Rosa Z. Owens.  Rosa was born 12 February 1882 in Maryland, Rosa was married to Frederick William Kosack but I have not been able to find where or when they were married.  Rosa died 5 December 1936.  These small bits of information on Rosa are only due to the information on her tombstone.  According to the story from my father, Rosa was in St. Elizabeth's Hospital in Washington, DC when she died.  I have searched Maryland, Virginia and Washington, DC not only for her marriage to my great uncle but also for her death certificate.  Family Search, Ancestry neither of them have her.  I have tried various spellings to no avail

Uncle Fred and Rosa married some time between 1900 and 1910.  They were listed as married in the 1910 census but in the 1900 census Uncle Fred was living at home with his parents and was listed as single.  Also in the 1910 census Rosa was listed as having 2 children and neither were alive.  I never knew Rosa and never heard anyone other than my father talk about her. 

I know that Uncle Fred had remarried and his 2nd wife I know a great deal about.  I have yet to find a marriage record for them either.  I do have death certificates for both of them but Rosa is a really big question mark that I would love to solve. This is the only photo I have of Uncle Fred & Aunt Rosa.  I have
no idea when this was taken.