It sounds as if your daughters friend might have left leaving the unit damaged and either blamed your daughter or the landlady has been unable to collect from the tenant.
Thus, she's trying to collect from your daughter.
Crossing off the former tenants name on the lease and adding your daughters name does not make this a legal document. Your daughter did not sign the lease.
Frankly, I doubt if this woman has a leg to stand in attempting to collect money from a tenant that was never on the lease and left two years ago. It sounds like a "bluff" that may also include a threat to file in Small Claims Court over this matter.
Gail