I Am Taking Over A Lease For My Sister. She Paid A $350 Security Deposit And A $350 Pet Deposit. The Landlord Wants To Change On Our Lease That The Security Deposit Is $700 And She Wants Us To Pay It To My Sister. Can She Legally Do This

Why is the landlord involved? A Sublease is between you and the leasee. While a landlord may have to give permission to allow the sublease, the lessor is YOUR landlord not the property owner.

If your sister doesn't want to charge you a security deposit she doesn't have to.