@Trips
We can't say for sure that Legosi's mom believed he wouldn't change.
If we think of this interaction as either real or a hallucination, I'd go with the hallucination.
There were two significant events that were revealed: Legosi's mom checking his face for mutations, and his mom hugging him in his sleep the night before she killed herself. Legosi's mom presents these two events as things Legosi doesn't know, but the author seems to go out of his way to show that Legosi
did know about them.
Because the main discussion consists only of things Legosi already knew, we can figure that he's not talking to an actual manifestation of his mom, but just his mind's representation of her. The part about her being content that Legosi would be okay is all an assumption made by him, as a way to cope with his mother's death.