It sounds like your boss takes her stress out on others. It doesn't matter to her what you were told when you got hired, even that you were on paid vacation, all she cares about is covering the work that needs to get done and how it affects "her" if it isn't done.

It isn't always you, often it is how others behave and deal with their stress and just happen to take things out on you.

There is this doll called the "dammit doll", my daughter has one and it's just a stuffed odd looking doll that when stressed/angered you can wack it around. Well, it looks like your boss uses you as her dammit doll. And if it was not you, she would do that with someone else, because she doesn't care about you, she cares about her own job security.