Any strategies to deal with cock blocks?

I'm trying to get something set up with a girl right now. Everytime I try to set something up, her cock block friend challenges my plans with a "girls night." I am never invited to their plans, so I never get the time to spend with her. Her friend also is saying negative things about me behind my back.

I'm thinking of calling the girl out on this or issuing an ultimatum.

Suggestions?