I did a search of the ancestry.com City Directories database for St Louis, Missouri. The search parameters were First Name=Nina, Occupation=Nurse. The results show a Nina Keltner, nurse, resides 1531 Pine in the 1895 city directory. The 1895 city directory shows a total of 6 individuals with the first name of Nina; only Nina Keltner is a nurse, 4 are married, 1 is a clerk. The 1897 city directory does not have a listing for Nina Keltner. Ancestry.com does not have the 1896 city directory but you could get a copy on microfilm from the LDS Family History Library. I did some other searches for Nina Keltner but I was unable to find anything to link her to William Burroughs.
David in Pennsylvania