It sounds awful. How much is she there when you are? Are you babysitting while she works at home, and she's home because her boss makes her work alone? If so, you have no option but to look for another job asap. If you are somehow lingering around the house when she gets home, I'd cut that to 5 minutes of transition time and then get out. But if you are hearing her yell for 2 hours, then that's not an option and she must be working at home, right?
I don't know if she's angry, mentally ill, or looking for attention - or all 3 - but you cannot help her or fix her. If you've already told her that she's difficult, you've done all you can. Obviously you cannot use her as a reference, but if the husband will write you a nice one, that would be great. Be careful how you word that, because asking for a reference will tell him your plans, and he may tell her, so the anger will escalate. Maybe you have to save up, quit, ask for a reference, and then start looking. If the older children can read, you might write them each a little note about how you love them but sometimes people get new jobs (closer to home, different hours...whatever you can say to help them know you aren't abandoning them and they haven't caused it, because they hear enough of that as it is). For the toddler and any other pre-readers, you can make a little picture of the 2 of you with a heart on it.
Sorry it's come to this.