I would not put her in the crib anymore. She has outgrown it and you are setting her up to pull this poop and pee stunt for other perceived offenses. So take her out of the crib and if that means shorter naps, so be it.
Continue to model good behavior towards her brother, even if it kills you. Decide where you draw the line, though. When she crosses it with him, like hitting him or knocking him over, put her in her room for a 15 minute time out. She will fight you tooth and nail over it at first, and things will get worse for a while. When she sees you really mean business, things will start to get better.
When she is older, talking through things will get you somewhere. Right now, she isn't going to really listen. She's jealous of him and that's that. But you must protect him right now and you must separate her from both of you so that she learns to want to stop, in order to not be separated.
Putting her in her room will also help you not yell at her - in a way, it also serves as a time out for you. When she has NOT crossed your line, instead of saying "NO" to her, say "We don't take toys away from other children".
Yes, 3 year olds DO take toys away from other children. They don't really play together - they parallel play. But you still work with them on it until the light bulb finally goes off.
Good luck with all this. I promise you that one day, your not-so-little guy will haul off and let her have it, and it will probably be the last time she hits him or knocks him over. She will finally learn her lesson.
Dawn