SOLVED. Adult or possibly YA, contemporary language, fantasy setting: librarians recovering old books and artifacts, libraries have doors to parallel worlds. [s]

[David]

Starts with young woman whose parents were librarians, born and raised in the library. Encounters an antagonist which provides the major plot. Several adventures which serve as steps in development of the plot. If I recall correctly, there are more than one volume.
I encountered this in 2015 or later. The language is contemporary, so I do not believe it is very old.

[Jessica]

The Invisible Library?

[David]

Yes, that is it! Thank you, Jessica!