Another possibility is that Irene may be responsible for Clare's death. She seemed to be growing quite jealous of how friendly Clare had gotten with her husband and she was clearly the most shaken up by Clare's death. During John and Clare's confrontation by the window, Irene is shown putting her arm across Clare when he runs towards her, though it's not clear if she was simply protecting her or if Irene actually pushed Clare towards her death. It's also worth noting that when everyone made their way downstairs to check up on Clare, Irene was the last one to head down and she immediately lost it when police began questioning her.