Transfer of Property in Pagdi System through NOC from Sister - Can NOC be challenged

Dear Sir, I stay in a Pagdi system house in Mumbai. The house was in my grandfathers name who has only one daughter who is my mother. My mother has 2 kids, myself & my sister. I took NOC from my sister few years back & got he house transferred on my Mother & my name jointly. Later, my mother gave her affavadvit to transfer the house on my name & i got the house transferred on my name only after a year of the first transfer. The BEST electricity bill is also on my name. Now, my buliding is going for re development and my sister has written to the landlord not to transfer the rent receipt on my name as she is unaware that i have already executed the transfer of the house on my name. She writes to the landlord not to enter into any agreement with me for alternate accomodation, rent for the same without her consent. Can my sister come back after all these years and challenge the NOC given by her on the basis of which i have done the transfer of the house on my name. she alleges that i have fraudently taken her approval on the NOC which is a false claim by her. she has signed on those documents herself in presence of all family members and now she is denying it. What is the legal implication in this case for me ? Should i write to the landlord or my sister lawyers stating all the facts of the case through a lawyer as the new landlord is not aware of the previous transfer as he has recently purchased the property from the old landlord. Or in the alternative should i only simply write to the landlord informing him of the facts of the case and do not reply to my sister's lawyers notice as she wants to just haress me now. Kindly, please guide me in this case to resolve this matter amicibialy as i do not want to get involved in any legal or court issues where i have to spend considerably time & money. Thanks.