I can't bring myself to remind my boss about paying the severance package for a woman she fired
But they need to pay it, so why don't you want to remind her about paying that severance package?
I think that if she pays her then the word will spread and others will try to abuse the system
I can see your point, but I believe that you need to behave professionally in situations like that. Do not ignore your obligations and tell your boss what she needs to hear. Otherwise you might be identified as unreliable and not a team player and fired.
I feel good about it.  I don't need to care about my coworkers.
Not following through on financial obligations is unprofessional, and you shouldn't feel good about it. That woman is waiting on that money to pay her bills. If it's your job to remind your boss about paying it then don't you think you should just get it done.