She's a moron basically...
She probably just wanted you to stick around until it was convenient for her, but since she saw you with another chick she got all mad that her rebound guy was spoken for or whatever she thought you were. Kick her to the curb.
'11 BMW E92 ///M3 - ZCP and DCT
'15 Ford F-250 - Lariat, 6.7 Powerstroke Turbo-diesel