If she did that then that would have added more fuel to the health scandal conspiracy.
"Oh see! She's dying; that's why she had to stay home even though the 9/11 memorial was taking place. Or maybe she doesn't really care about the victims!"
There's no way out.
More fuel than being caught on video collapsing while stumbling into a van? I don't think so. If she stays home and tells the truth up front, there's no viral video showing a physically weak woman stumbling out of the 9/11 memorial service. There's just someone who stayed away from the ceremony because she had pneumonia or is feeling under the weather or whatever the Clinton campaign tells the press. This being on video adds even more fuel to the health rumors because there is now video evidence.
It usually helps to get ahead of bad news, not behind it, like the Clintons seem to always do. Claiming all is well and Hillary is completely healthy when she is not doesn't help things for her at all.
It doesn't matter. When facts don't fit the narrative, they make something up or invent a new narrative. Or they can take photos and videos that are harmless and
use them out of context. She cannot win.
No one's been subject to more scrutiny than the Clintons have. If you were under public surveillance 24/7, you would probably feel burdened to calculate the way you live your life, too. So of course Hillary wouldn't want to open herself to things that have the potential to bring unnecessary controversy. Unfortunately, it happened anyway.
As Arch said, there's no way out.