Is Monica liable for the remaining lease payments?
This is because she did not formally or legally transfer the lease to Tony since her lessor (The landlord) was not involved when Monica had an agreement with Tony. Under a typical lease agreement for one to transfer a lease, the lessor must permit the transfer completely to someone else or they allow you to transfer the lease provided you remain named on it. Also when transferring a lease one must submit a request to the landlord for consent and Monica did not do this. Monica did not legally transfer the lease to Tony and since signing the lease makes her legally bond then she is liable for the remaining lease payments. For Tony to be liable he must have signed an assignment agreement and the landlord should have qualified him as a potential tenant.
Yes, Monica is liable for the remaining lease payments.