The Deceiving Co-Worker

Alright ladies.. I work in a bank part time that is open on Saturdays. As a part time employee, you are told in your interview that part of your schedule is working EVERY Saturday. I have no problem with this. It's 9-1, not a big deal. My boss recently hired a girl back in February. Before you begin working, you must complete a 2 week training course. She was enrolled in the training & called out of every class. So they had to reschedule her training.. out of that rescheduled training, she attended 5 classes. So all in all, she had about a month of training. She comes into work & is put with a leader & trained with her for 3 days. It is June & she still does not correctly know how to do her job. Her coming in literally puts a hindrance on the rest of us. We all have to constantly stop what we're doing to show her how to do the simplest of things. She does not pay attention to anything she does & when she is corrected, she tells US* that we do not know how to do our job. She also does not own up to her mistakes.. she put a customer's account into the negative by $300 & when asked about it, she blamed it on a co-worker when we had her numbers for her log on right in front of her! She also has made comments that she doesn't need this job because her husband owns his own company. & on top of all this, she calls out at least twice a week. In addition to all this, she refuses to work Saturdays.. she says that it is "unfair" when she was told (as I previously stated) in her interview that Saturdays were part of her schedule & when asked if that was okay, she said yes. A co-worker found her on Facebook & saw where she had been posting things on the days she called out saying things like, "Got 'em again. F*ck that place!" or "Lazy day for me today!"... my boss however has been trying to give her the benefit of the doubt but I don't know how much more I or any of the other ladies I work with can stand. How would y'all handle this situation? I feel like I'm about to lose my mind.