Joe's Mom is (obviously) the mother of Joe and Anna. She is also the sister of Uncle Joe and Mad Jack.
In the book series she is portrayed as a short tempered woman who was once the owner of the book herself. In the TV series however she is not portrayed as someone who is involved with the book. No doubt though she is very much aware of what it's true powers are.
In the book series she was the one who gave the book to her brother Joe when he was 10.
Though her children knew about their Uncle Joe, neither she nor Uncle Joe told them about their other brother, Jack.This is probably due to their estranged relationship do to him being evil.