Ask her how you can help her, different times, different triggers, perhaps many things and often she may have anxiety over something you would never imagine. You are a great BF to her for asking for help, may she know how lucky she is to have you. If you ask her to describe things that happen to her when she's experiencing the anxiety then you can be watchful and do what she needs when she's becoming anxious. Offering to go to T with her, is wonderful and very supportive. You are one hell of a guy to put this question out there and wanting to be so supportive of her.