The Nuclear capabilities of Israel might mean that arming the devices was time consuming. Possibly an order to prepare for their use would have to precede their intended readiness date by a few days. But if Meir hinted to the US that she was prepared to nuke some capitals, I would think the US would do all it can to stop this. Hence massive conventional aid to Israel. I do not doubt Israeli ruthlessness.
Peru forces rescue 54 adults and children held captive by Shining Path (AP)
from the article: Did Israel ever consider using nuclear weapons?