Arvens, it was a movie. It IS guaranteed that she would have been on the other side of the divide.
Plus, just like Littlefoot's Grandparents, she would have had to accept the other creatures as they were. Why should it have to be Littlefoot who never saw his mother again, whereas Cera, Ducky, and Petrie all had families to go back to. As for Spike, well, until LBT, he showed no discontentment.