It would be funny if the girl did in fact receive recs from profs and told you she wrote it just to play on you lol One should never trust what people say;p It is really hard to believe she would do it and then told you so. I think you should not jump into conclusions and should not accuse her of forgery (as your topic is titled) - this should be decided by authorities. Calling schools and telling them she forged recs is a bad way - if it happens she just joked then you may be in trouble. You did not see her forge the letter - all you know is what she told you and she may as well be making it up (no idea why would she do so, stress maybe?).
Nevertheless, there is a probability she did forge it so you could talk to authorities (be it chairman or someone else) and tell that person there is a possibility of forgery and then explain what happened and let them decide if it's just a joke she played on you:P Just be sure to word it carefully. And don't get me wrong - I am 100% against people who cheat but I also am careful in interpreting stuff;p