Did you not also see her Secret Service detail rush in front of her? I suspect she was rightly focused on a potential threat in the crowd.
GWB has the same "stare" in the infamous Iraqi shoe-throwing incident.
Yeah I don't think I'd read too much into the "keep talking" thing. Something is going on in front of her... her people are handling it... and they just tell her to continue her speech and ignore it.
There are some legit health issues to look at with her... and then there are things that are a bit embellished.