This is somewhat critical issue. It seems to be like that you had no legal contract with this girl. You need to do a legal contract before doing such ad with models. Now, I don't understand why she is asking like this? Is there any unwanted pics on Facebook or on calender? If not then there will be no issues. Try to discuss this issue with her and try to find out any alternative solution on this. Even thou she is not ready for the discussion then it need to fight against legally. But still I think she can not do anything. All the Best.