I can't decide between 4 and 10, cause in both she's crying because she is about to lose something very dear to her and neither she nor US know what's gonna happen. In the fifth we could be reasonably certain that the kids would be returned, but in the Fourth they could just as well have killed off her hubby and in the tenth it could have been reasonable that Littlefoot went with his father instead of them

As for why she is the one crying? Well, in the first one, Grandpa wasn't exactly in a position to cry, while in the second he might have been trying to stay strong for everyone's sake considering he DOES have a leaderposition, regardless of how they make their decisions. As for the third...

dunno xD