In the novel, Mildred does not die as we read. She leaves in a taxi to go somewhere, with one suitcase...Montag—in his mind's eye—imagines her in her hotel room.
He imagines that just before the bomb drops on her hotel, that she might in the split second before her death, look into a mirror and see herself as she truly was rather than how the society brainwashed her, and everyone else, to see herself and her place in society. She would see the reality of her non-life: breathing and acting as if a robot.
Members of society were expected not to think, not to question. And books were banned because they were counter-productive to this desired behavior: books generate ideas, and ideas generate higher-levels of thinking and a desire to change.
As the above educator notes, Mildred has an epiphany while she is watching the television on the walls in her hotel room. As a bomb drops on the building, Mildred sees her own reflection - a "wildly empty face" - and suddenly realises that the television shows she holds so dear amount to nothing but emptiness. Furthermore, the "family" do not love her nor will they ever be anything more than a projection on a blank wall.
The real significance in this epiphany, however, lies in the fact that it does not really happen. It is simply a product of Montag's imagination, something that occurs only in his consciousness. What is more important is the function of this epiphany as a symbol of Montag's hope for the future of society. Montag is optimistic that people who are hooked on entertainment, like Mildred, will eventually realise its damaging effect and discard it.