At a distance where your nervous pup is comfortable, show her a treat. Now, walk with her toward the dog run and stop before she stops. Stop, praise, treats, retreat. (if she stops first, retreat quietly and try again). Repeat. As she links getting treats with being nearer the dog run, she should be willing to go closer. If she is, great. If she isn’t, no matter. Just park yourself on a bench nearby and read the paper. Let her watch and learn.