The rebel offensive is the strongest in almost 10 years of civil war, in which 70,000 people have died.
A rebel offensive in November showed that neither side was close to a military victory and increased pressure to negotiate an end to the war.
Her arrest came during a major rebel offensive in the Salvadoran capital.
By 9 October, the rebel offensive against the base had bogged down.
The rebel offensive seems to have raised the level of the decade-old conflict.
"I'd say we've run right into a rebel offensive," Jeffrey said.
The combat was set off by a rebel offensive in the working-class and poor neighborhoods around the capital.
In early January 2013, reports emerged that the military had prior knowledge of the rebel offensive.
He said the rest of the staff "ran away" last week when the latest rebel offensive began.
A battle near the town stopped a new rebel offensive in May 2009, with more than 200 reported deaths.