Should the truth be told to Erin, she will ask for the Sole Survivor to go out into the wastes and look for her, stating that Ashes would be scared, and would not wander far.
The Sole Survivor may choose at this point as to whether or not to lie to the little girl, or to tell her the truth.
Erin Combes, Ashes' owner, will be seen looking for her cat that had run away after scratching her.
She could have not gotten too far away out in the wastes. After scratching her owner and being scared away from her shout from pain, Ashes the cat runs out of the vault in fright just as the vault door opens to allow the Sole Survivor in.