Continuity mistake: When Abby is wiping the table at the start, her hand position jumps instantly. (00:04:15)
Continuity mistake: After Senator Kiley asks Gibbs to keep his name out of it until after the vote, it cuts to Ziva holding Carrie McLellan's Academy graduation photo (gold frame looks like an 8x10). In the closeup Ziva places the framed photo back on the shelf, but that photo vanishes from the shelf in following shots. When Gibbs walks in, it seems that photo is on the table beside the couch. (00:07:30)
Chosen answer: It is never stated, however she must have been there several years if she is on presidential detail.