I thought Mama McG was less abrasive in this episode, but the whole story tracks so weird. First she's in hiding for years, then she's afraid to come back because of Wo Fat, then she sees him and he escapes, and now she's fine with him being on the island. If she knows him or he is her son, why was she so afraid to come back in the first place?
My thought was that she probably told Wo Fat the truth that she is his mother when she confronted him in the room, and now feels that he won't kill her as a result, or will at least be conflicted about it for a while. Up until this point, I think Wo Fat simply thought she was the spy who killed his father, but had no idea that she was actually his mother as well, which is why he was so determined to kill her at first but then had a change of heart. So now she feels confident about being able to remain on the island safely, although that could be overconfidence on her part (a trait both McGarretts share).