Two more cents from another librarian. Find out if your library has a meeting room policy stating who can and cannot use the library, how often they may meet, etc. This will give you valuable information on whether you need to lobby for the creation of fair policy, change a current policy, or remind a librarian that she needs to follow an existing policy.
Also, the American Library Association has established both a library
bill of rights (check out article VI) and a library
code of ethics (check out article VII), both of which should aid your cause.
When I was a kid, my public library either hosted a D&D game, or allowed some older kids to use the meeting room for a game. I thought it was great, got all excited, and soon thereafter bought the basic set. A few months later, though, I learned that the librarian had done an about face, bowing to pressure from those who opposed the game on religious grounds.
Good luck!
Get thee to the dungeon. Get thee to the dungeon forthwith. Pass not the barbican. Amass not 200 GP.