Lort, I know exactly how you feel. My Mother (a sweet, stay at home Christian lady) turned into a woman who could/would bite, pinch, spit, and had a vocabulary I had never heard. She would say "if you loved me, you wouldn't put me in a place like this", anything to cause me to feel guilty.
Most days I cried on the 15 mile drive home. It was the most exhausting 10 years of my life. Daddy (a medical doctor, who had cared for Mother, had a severe stroke, which left him unable to turn over, eat or speak) was in the same skilled facility and lived for 7 years. However, his spirit remained sweet and cheerful.
BTW: after I had tried this ploy several times, one day she looked up at me with twinkling eyes and said clearly, "am I being good enough for you to stay awhile". I laughed and went out and got us little ice cream cups. The mind is such a strange thing. Alz./ dementia patients become very cunning and the trained staff understand this better than we, the family. Does she like sweets...some treat? Bribery works. Also, would she hold a doll, love it, dress it?
And as you love her, you must take care of yourself. She is your big, little child now. Treat her with kind, loving discipline. I know with job, family, it is so very hard, but also treat yourself with some kind, loving also.
My thoughts are with you