Do you have any idea what precipitated her fear?

Do take her outside for walks for a half an hour after she eats, and stay out until she does her business. As soon as she eliminates outside give her a treat, and lots of praise. No lap time outdoors until she has done her business, as cruel as that may seem, coddling her will reinforce she should be afraid. Be patient - even bring a book with you to be able to outlast her outside, and praise praise praise. Take her out for a short walk, the next day a longer one, and even longer. work on any commands she knows when you are outside, run her through sit, down, stay, spin - whatever she knows so she associates being out there with happy things, and with a "job" to do.