The Question and Answer section for The Hound of the Baskervilles is a great resource to ask questions, find answers, and discuss the novel.
Can you please re-state your question?
Mrs. Barrymore is Barrymore's wife, and Selden's sister. Watson remarks that she seems to cry often. He thinks she could be hiding something.
Rather than writing the whole thing out again, you can check out the chapter 12 summary which will explain everything: