http://en.wikipedia.org/wiki/Sad_Cypress
Role of Elinor can be assigned to Tara who would be accused of murdering JR 😆 Mary's role can be given to nandu... & Nurse Hopkins can actually be kala who escapes after being exposed by MJ & Tara or aid of kala can come as Nurse Hopkins. They can bring some new entry to play the role of Poirot or MJ can don the thinking hat...😆
As per this idea Tara won't be a suspect till Nandu dies. Nandu will the prime suspect of murdering JR but after Nandu herself gets killed by poison Tara will be the prime suspect.