I have been an active member here for a while but spend most of my time in anxiety or the depression forums. I am not familier with PTSD so I need some advice.

My best friend was diagnosed with PTSD a little over a year ago. She gets extremely upset about loud noises to the point of hysteria. Last week we were having fire drill testing in my office building and they were going off nearly all morning. My friend was so upset by thing that everytime the alarm would sound she would well up with tears and ask me to excort her outside until the testing was over. She was so upset by the last test that he was shaking, literally shaking. She said that she was so afraid that something bad was happeing and I didnt know what to do. She ended up leaving work early because it was too much for her to handle. I didnt know how to help her. I didnt know how to calm her or convince her that everything was going to be ok.

Is there anything I can do for her? I stood by helpless and feeling guilty for not being able to do anything.