Is there any other way you know of to make a sim cry on demand?
You could try to give them the "neurotic" trait and let them harvest a death flower (on the home lot, not the cemetery). Other plants work as well, but with death flowers, you can be sure that they die once harvested. No guarantee, but the constant crying over barren plants was the reason why I stopped making any sim neurotic.
Oh, but make sure that it's the only plant they harvest (or the last one). It doesn't work when there are other plants still queued up.