Just some clarification. If you are using it as such, the branch's category is HSSD. If you are using HSS as a larger subject grouping, then I would suggest you put all the subjects in HSS and only put the subject categories on the relevant pages. Sorry if that sounds confusing.
Basically, if you mean to use HSS as a topical subject (rather than referring to the library branch), I suggest creating the "Humananities and Social Sciences" category then adding History, Women Studies, Literature, etc. as subcategories. You would then only add the relevant subjects to each page rather than having to add all the pages to both H&SS and the subject(s) (which would be the equivalent of adding, for example, Finding Library Materials and Microforms categories to all microforms pages rather than only adding the most specific one i.e. microforms).
Let me know if you have any questions or comments.