That's a hard place to be. I would try rewarding her for being quiet, and completely ignoring the whining. No attention whatsoever for the whining, aside from a single "That's enough, Sorcha" when she starts.

It's something I struggle with, because Summer is a barker. We're doing better, but sometimes I wonder what the neighbours think, because if I give in once, the next time she keeps going even longer before she remembers nothing good will happen if she keeps it up.