Because there seems to be a wrinkle:
An attendee later handed a reporter a piece of paper that was apparently thrown by the woman. It appeared to be a copy of a Department of Defense document labeled confidential and dated August 1967; it referred to an operation ‘Cynthia’ in Bolivia.
“Operation Cynthia” seems to be a hole in Google. I cannot find any good info on what Operation Cynthia was. There’s a Time magazine article from 1967, but it’s behind the paywall. Wikipedia is mum.
What this has to do with Hillary mystifies me.
UPDATE: Sean pulls the veil back some:
A library card is a powerful thing. Operation Cynthia was the name of an anti-guerrilla operation ordered by then-President Barrientos and conducted by the Bolivian military. The target was a group of pro-communist militants who opposed the standing government of the time and who appear to have had close ties with Fidel Castro in Cuba. The operation was named after the commanding officer’s daughter.
According to Wikipedia, Barrientos came to power “in a CIA-backed coup”, whatever that means (did the CIA say “Hey, you, get rid of this president and we’ll back you,” or was it more like Walder Frey asking Tywin Lannister for approval before the Red Wedding?). The article doesn’t substantiate this, and indeed suggests that the charge originates with Barrientos’ erstwhile frient and Minister of the Interior, Antonio Arguedas, who fled to Havana with Che Guevara’s diary after Bolivian troops captured and killed Guevara. So there’s that.
One might safely assume that the Johnson Administration would have provided support in some form for the combating of Marxist guerrillas in Latin America, but this remains an assumption.
What was Hillary Rodham doing in 1967? Near as I can figure, this is about the time she stepped down as President of the Wellesley College Young Republicans, and moved to supporting Eugene McCarthy’s campaign. So…
Content Blues 
A library card is a powerful thing. Operation Cynthia was the name of an anti-guerrilla operation ordered by then-President Barrientos and conducted by the Bolivian military. The target was a group of pro-communist militants who opposed the standing government of the time and who appear to have had close ties with Fidel Castro in Cuba. The operation was named after the commanding officer’s daughter.
I’m not sure how that ties in with Hillary Clinton, since the Time article is from 1967 and makes no mention of US involvement. But if you wish to research it further, the names Guide and Roberto Peredo, Antonio Negro, and Jules Regis Debray may provide additional leads.