There is really nothing you can do. The heart thing may be separate from the diabetes. But sugars out of control eventually do kill people, one way or another. I'd just steer clear of the subject with her.

One cannot make people in denial do anything when they are like this.

I know a prominent DOCTOR here...a woman no less... who ignored her diabetes, for years in denial. She dropped on her porch with ketoacidosis and it was too late for her. She died.
She was a child psychiatrist no less!

This person you describe seems to have no pancreas left to fall back on. When that happens only injections will work. Making some people change food is the hardest thing. Food may be all she has emotionally!

People in denial, like that must have deep seated esteem issues, and perhaps are looking forward to death.

Changing diet at this point, may not accomplish much... in her mind's eye... so she keeps her food where she likes it. It is not likely she will ever be off insulin.