I'm sure sometimes God does heal people.
But why cancer develops and how it develops and whether people get remissions and why sometimes people can actually cure themselves is very complex. This is partly because it's not a part of a body which gets sick but a whole person.
It's unlikely that your aunt is going to get better this time.
What usually happens with cancers is that they start with a fairly benign line of cancer cells which is not too hard to control.
Then somehow the body's controls can't manage any more. For example, every million or billion cell divisions in a breast cancer is a mutation (change) and those mutations tend to get more aggressive than the original cancer. That's why the cancer grumbles along and then all of a sudden there's a 'daughter colony' which is much more aggressive. That daughter colony then forms a new cancer and behaves quite differently from the original illness and it takes over.
Then the cancer is much harder to treat. It might continue to spread around the body.
This happens with all sorts of cancers.
So when someone gets cancer for the second time they usually die from it.
But not always.