I have watched a movie several times over the years and would like to purchase it but can't remember the title. A women is married to an author, and her sister visits (or lives with them?) and the women because jealous of the relationship between her husband and sister. At one point, he dedicates a book to the sister. The women dies of poisoning (following a picnic?) and the sister or husband is suspected. I think it turns out that she poisoned herself and framed them. The husband and sister end up together. Anyone know the title?
