Mrs. Joe has been hit in the head and obviously has suffered brain damage; therefore, it is difficult to assign a reason to her reactions when she sees Orlick.  One reason for her smiling at him may be that she recognizes him and attempts to express something. However, when one does not have control of one's muscles, a grimace may easily turn in to a smile. So, Mrs. Joe's seemingly happy countenance at the appearance of Orlick may not be gladness at all.

Mrs. Joe develops a strange liking toward Orlick because he is the only person who ever stood up to her. Unlike Mr. Joe and Pip, Orlick is not truly afraid of Mrs. Joe. While the attack on Mrs. Joe changes her completely, the "attraction" she has for Orlick is only based upon his ability to stand up to her.