I heard that if you blow up Megaton with the "Atom," you can go back to the destroyed ruins and you will find Moira (Craterside Supply Owner) wandering around as a ghoul. I blew up Megaton and I waited around the ruins, but I found nothing but huge loads of radiation that end up poisoning me. I took care of the radiation problem with 100 Medicine skill and Rad-X but still haven't found Moira? Does anyone know if there is something specific you have to do/complete to trigger her appearance as a ghoul?
From Fallout Wikia
If you decide to blow up Megaton, she will not die; instead she will become ghoulified. If you started the Wasteland Survival Guide quest, or met her to receive an armored Vault jumpsuit, you will have to visit the Megaton Ruins to find her. If you hadn't started it, she can be found in the Underworld, whereupon she will claim she was 'out-of-town' during the detonation, and apparently unaware of her recent affliction. Depending on how you break the news to her, she will either fall into despair or remain positive. Eventually, she will leave for Rivet City and finally Underworld.
I've had my own experience with her.
I just walked up to the rubble and she came out of no where. She didn't know she was a ghoul until I told her and after she said she was going to Rivet city.
After she goes to where all the Ghouls live the Underworld.
It matters how you tell her too. She nay be depressed or happy. And she says she had more excuses to travel the wasteland.
If you talk to her at the ruins before she engages you in conversation she often becomes bugged and will stay at the ruins without moving to Underworld and only repair items, not buy or sell them.
I fast-traveled to the Megaton Ruins after finishing the Power of Atom quest, and found M. Brown walking around as a ghoul. I engaged in conversation, but I was only met with dialogue choices regarding the android, repairing items, and, of course, saying "goodbye."