T.S.
Don't push it. Remind her to use the potty at home before you go out, then try to avoid large amounts of fluid while yo're out. Without suggesting that she use it, invite her into the bathroom stall with you. Let her watch you use the potty and ask her if she would like to help you flush. If she feels in control of the flush, she may be less afraid of it.
If her fear is becoming more of an issue it might be worth a trip to Home Depot or Lows. Let her examine the toilet plumbing... touch all the parts etc. Once she understands that it is just the sound of air and water moving quickly through the pipe, it may be less frightening (ie not some growling monster who is likely to grab her as well as the poop!).
Good luck with this. Hope this helps.
T.