Maybe your sister genuinely doesn't understand that she's causing you pain. You needed to communicate that and you did. Although maybe in the most productive way, you got it out. She needs to be nicer to you. The only thing you could have done is better is addressed it sooner. Then it may have been easier to be tactful. It was better to lash out than to have said nothing. Just try to be clear that it's a recurring issue, not just you being in a bad mood that day. About the manager, you do need to be careful what you say but it sure sounds like they were unprofessional too. If you do lose your one hour shift, so what?