Ok, Cera, at least until the Hidden Runner episode, always denies she is afraid. One might think that it might be stubborn "I'm a Threehorn and Threehorns aren't afraid of anything!" attitude. But there is another possibility that I'm not sure if anyone has brought up yet. As the incident happened in the first film, I thought I'd put it here.
As you know, Littlefoot saw directly what happened to his mother. However, Cera also saw the attack. (Littlefoot may have been more affected as it was his mother and he actually saw her die (Cera didn't see what happened to her own mother, whatever happened to her.).)
However, Cera was so young at the time and that HAD to be a lot for her to handle. Maybe her "I"m not afraid!" attitude is some weird coping mechanism due to the trauma of Sharptooth's attack and being separated from her family during the Great Earthshake and the close call with Sharptooth she had a short time later in the canyon. Not to mention the second attack of Sharptooth later with the others. And then there was the time she got attacked by the Fanged Flatteeth (Domeheads). And she got rescued...by a tar monster.
True, knowing Topps, one can argue that the Tree Star doesn't fall far from the tree in terms of how Cera ended up always being so tough, but it's a known psychological fact that people who go through trauma can be unusually tough and hardened and want to appear that way as a defensive mechanism.
(I think Littlefoot may gotten his "I'll make friends with anyone that doesn't try and whack me." attitude as a coping mechanism, as he just wants friends as he's so hurt by what happened to his mother.)
