She probably doesn't elaborate on her death because she wants the reader to think about the REASON that she dies more than the actual death.
The point of the story is that Mrs. Mallard dies, not because she is so sad that her husband has died, but because she is so upset to find out that he is still alive. During the time period when the story is set, women were thought to be very weak so it was assumed that Mrs. Mallard, who is sick with heart disease, would not survive learning that her husband has been killed.
On the contrary, she is actually relieved when he dies and the shock and disappointment of him being alive is what kills her.
It is this irony that the author wants the reader to focus on rather than the details of her death.