Julieann,
I would suggest that your mother make an appointment for blood work. Pat has mentioned many times about this B-12 deficiency and it really holds a lot of weight!
Also what medication is she on? There are some that can effect Memory too. My husband couldn't remember if he called his mother on her birthday and was so upset...he did call her but it really bothered him that he could not remember it at all.
Is your mom on an anti-anxiety medication like Xanax or Valium, Ativan? They do help her to even things out so to speak.
Lastly, Your mom also knows that she is dying...there are a range of emotions involved
in that alone. She is going to have good days and bad days physically and mentally. You shouldn't judge her for it. But you should be prepared for it. She will lash out at others, but primarily those closest to her. Think of it as a compliment of how strongly she feels. I know that sounds strange, but this whole process is a learning experience...one we don't want to learn, but will regardless.
I hope this helps somehow,
Karen