My daughter lives in California with 2 roommates in a condo. She is transferring to a job out of state and the landlord has told her that she must secure a new roommate for the condo. Other wise she will be required to pay rent until a new room mate is found. Is this legal in California?

Depends on what the lease said. If your daughter signed a lease with that clause, she is liable for 1/3 the rent.

Hello a:

In whose name is the lease written?

excon

If she is liable for her share of the rent, and is on the lease, yes that is normal, if you rent you are bound by the lease. And you will continue to pay the rental till the landlord finds someone. *** except for Florida they are required to try and find someone. ( but after the person moves out)
So if they do not want to wait till after they move out, yes they need to help find someone.

This is very common.