Agreed. And was she not at the event in an official capacity?
If someone's job is to be a public figure or spokesperson for a given company then everything they do publicly online is relevant (I'm a huge advocate of using pseudonyms and anonymous communication online over personally identifiable communication.)
In the current day & age, for better or worse, you have to be very acutely aware of your "surroundings" -- that includes what you post on any social media website, and especially if you explicitly name your employer.
IMO, and again, for better or worse, this does currently apply to both personal and business accounts as long as they're visible...