Adam's Mother is not actually encountered in-game, but there are bits of implicit characterisation treating us to some information about this person. From a conversation with Rebecca it can be speculated that Adam's mother is of Canadian descent and that the family had lived in Helston for a while before she and Charles divorced when their son was very young.
Adam: Rebecca, do you have any family? Rebecca: I did, a long time ago. Adam: Oh. Rebecca: I hardly remember them. What about you Adam, do you have any other family? Adam: Only my mother... My parents separated when I was very young. Rebecca: What happened? Adam: You know, people grow apart sometimes. Dad always had more time for the church than his family. Mother moved back home to Canada. I never saw Dad much after that. I met him briefly four years ago when I was on a student exchange. It was an awkward meeting. He'd changed a lot - but it was too late... for both of us. Rebecca: It's never too late Adam. Adam: Sounds like the voice of experience.
Additionally, one of the stained glass windows of St. Michael's reminds Adam of his mother.
Adam: The resemblance is uncanny. Rebecca: What do you mean resemblance? To who? Adam: My mother. Dad must've kept this close to his heart.