I had thought they were mother/son, but in last week's episode, when she asked him why he was fixing the clock, he said his father used to do that... which made me think, hm, she can't be his mother, then. Or if she is, that bit of dialogue was quite odd.
She's very good indeed! I really can't totally hate her or Thomas... I suppose I can't help but feel sorry for them, they are the only ones so openly frustrated, bitter and un-accepting of their lowly status.