I think she didn't know what her brother did..! Her husband spared her from that.! But when she went after Gideon and he didn't melt for her and she went back to her husband he may have told her..! ( she then put it together, he would of never stayed with her knowing what her brother did to him.)
So after her breakdown (if her husband told her what her brother did to Gideon) she realized why her brother killed himself, so her revenge is Corrine. ( To get back at gideon) So if in fact she is Corrine psych (and her husband did tell her about her brother) she knowingly fed Corrine those pills knowing the side effects ( most anti-depressing meds come with homicidal warnings) what could happen..!
Or if she doesn't know what her brother did and she is Corrine psych, she still mad at the iceman for sending her back to her husband and not not staying with her.,! So either way Anne Lucas is dangerous..!!