Its 1 moment in time. Stains are all night and make everyone uncomfortable.
She probably should have put pads in there; hot flashes are natural but on your daughter's wedding you don't want that in the pictures.
Here's the deal, though: Sarah was, at one time, a working senior member of the BRF: therefore she knew at some point how to handle this aspect of presenting oneself in public life, has access to the best of the best, has been there and done it, and therefore there's really no excuse.
What probably happened is that she was so wound up that she plumb forgot to put her anti-perspirant on.