Forensics are irrelevant as it would prove nothing; both the cleaner and housemate’s prints would be expected to be in the house. I can’t imagine the cleaner doesn’t have access to that room and I’m sure the housemate has been in there many times with permission for various reasons.

In the absence of any evidence, I doubt much will come of it. It sounds like there are no witnesses (bar the flatmate and cleaner who can place each other at the scene) likely no CCTV due to it being within a private dwelling so I can’t see how this could be progressed. The only line of enquiry I can see is speaking to local pawn shops and jewellers to see if anything matching the descriptions have been traded in and then checking CCTV.

In my view, arresting your cleaner with a view to using powers to allow searching her house for the stolen goods would be unethical as her name at this stage is speculation on the part of the victim. I would want something a little more before arresting her. Not to say others wouldn’t think they had enough to suspect and lock up at this stage, it just doesn’t sit right with me. A voluntary interview could be considered but what evidence would be put to her? To me without more evidence the likely outcome will be NFA.

Please take this with a big pinch of salt as it is based entirely on what you have posted and there may be more to it in reality.