Most of what I know is about enrichment, that is, ways to keep animals engaged and happy in an unnatural environment. For instance, cats benefit from toys that emulate hunting.

Grief, there's not much you can do other than pet them and wait it out.

Trauma has some treatments, like counterconditioning to break down triggers. This is much more effective and less dangerous than standard exposure therapy, which tries to grind away triggers by brute force (and can make them worse).