The worst time is when there are other people around and she does it, and DH and I don't particularly immediately react or start fussing over her, and other people grandparents start being all concerned, but they haven't seen her do this about a gazillion times before. Then we have to start justifying why we aren't rushing to her aid.
Obviously if she's genuinely injured we do look after her, but 99% of the time it's nothing at all serious.
When it's this frequent, is it best to be sympathetic, or to tell her to get over it and stop crying?