Think about any changes that have been made to the house or yourself.At 18 months Kashmira is now showing independance and may no longer need or want the attention she did a s a baby. Pay close attention to her body language and learn to understand when she wants to be left alone,they do sometimes want this.Has she become closer to another member of the family,they can change who the preferred person is and that person may be the only one allowed certain privilages such as petting.Try and avoid situations where you know she will bite eg if she bites when removing her from the cage let her come out on her own .