Tenant wants to sublet room in apt without landlord involvement

[Kathryn D.]

Hi!  I have an excellent long term tenant (7 years) who has gone through about four roommates since she has moved in.  The moveouts have been for usual life reasons (moving out of town, moving in with boyfriend or girlfriend). She is now in the process of looking for a new roommate and asked me if she could be the primary lease holder and sublet a room without getting me involved. She thinks this will give her the power to evict a roommate if needed.  Does anyone have any experience with this?  All I can see are potential liability issues if the new tenant does not sign the primary rental agreement between me and my tenants.  The rental is in Portland, Oregon. Thanks in advance.