She was in there from ulcers on her leg but have a long history of heart failure and they put her on a floor with no monitor. ...
Duecered, here is a link to the Cleveland Clinic on leg and foot ulcers, showing how some are connected to heart problems:
http://my.clevelandclinic..org/services/heart/disorders/pad/legfootulcer
Your mother's long history of heart and circulatory problems probably contributed to the ulcers on her legs. I do not know why your mother was not on a heart monitor if it was her heart that brought her to the hospital in the past, but her doctors can possibly explain that to you.
It still does not appear to me that your mother's death had anything to do with what the hospital personnel did or did not do when your mother was in the hospital to have her ulcers treated, but you can have her medical records reviewed by a malpractice attorney in your area if you think there is some reason to question the care (e.g, the lack of a heart monitor).
I agree with the others that your mother's age and medical history will complicate any findings. The DNR directive is another complication.
Again, I am really sorry for your loss. I hope you are finding comfort with your family members.