A new theory is that Suzy and Mary may have been having an affair before she died, and that this is why Mary feels so much guilt towards Vanessa.
Fans know that Mary had a thing for Suzy who was with Vanessa Woodfield, and she was shown looking jealous at the pair seemingly being happy just before Suzy died.
In the episodes since Suzy's passing we've seen Mary upset and talking of her close relationship with Suzy.
With Vanessa asking Mary to attend the funeral with her for support Mary looked a bit shifty.
Fans now think they have rumbled a huge secret that Mary is hiding from everyone, and perhaps Suzy was too.
