My sister got yelled at yesterday at work......

Yep, your sister is spoiled alright. She already has everything she needs in her job and when she get's a hiccup or a roadblock she would immediately quit. If she decides to change jobs then she would see the benefits she had on her previous job. Worse, she might even get a job that treats her less.

Try to do something to calm her down. Exert your influence to be smart in perople communication. Never give the last words to spark the yell, both at home and in office.

Yes she does sound alittle spoiled. But tell her to hang in there. Alot of places are taking pay cuts and if she reacts in a negative way they might cut back her hours since she did not take a paycut.

whaaaat? 10 hours a day without a proper break ensured? I would freak out and quit the job no matter whether I get another one next day I tell you.
Thats no proper way of handling your staff.
I am diabetic so I need my breaks. Granted, I commute 4 hours to work with trains so I have my breakfast while commuting and only am entitled to the lunch break but I will TAKE this break cause I need to get me some carbs plus relax from that frenzy for 20 minutes.

I'm thinking that your sister should be right happy to have the job that she has and that the owner liking her like he does and so on because there's so many out there that NEED that job but can't find one. She's lucky to have that many hours working, most people don't have that with their current job IF they have one. Another thing too, her boss might have had something happen and needed her but couldn't find her because she was on a "long-er" break and he just flew off at the spur of the moment and she happened to be the target. Not that it's right but that could be the case. Sometimes she has to bite the upper lip and take it for what it is because like you said, the boss likes her and didn't cut her pay like he did with the others. That says a lot right there alone!