17 year old daughter stealing

We are having a problem with our 17 year old daughter stealing money from our wallets. We have no proof, we have never seen her do it, the money just goes "missing", it has been going on for many months now. We have someone staying with us and she has just told us that money has been going missing from her room. We know it must be our daughter but when we ask her about it she of course denies it and even acts offended that we would even ask her. She says that "she would never do that" and she thought our visitor was her friend, but obviouly not if she will accuse her of stealing.
All of the advice I can find online refers to catching your child stealing. What can we do if we are sure she is doing it but have never caught her and she will never admit to it? I can't describe how I feel, I am annoyed that she would steal from her father and me even when we give her pocket money. But to steal from our visitor, I am so upset that she would do this. But she acts as if everything is normal, there is no remorse at being caught out. What can I say to her? If she will not admit it, how can I punish her for "something she didn't do" ? I would very much appreciate any advice. Thanks.

[meg613]

who is ur visitor?
you need to pretend u trust ur daughter. the next time she is going out ask her if she needs/wants some money... and give her some. if she feels you appreciate her then she will feel guilty....... also it sounds to me like you shouldn't necessarily trust ur visitor..

[penswriter]

get a nanny cam. have the wallets or purses in a general area near the nanny cam...it will catch your thief. if it is your daughter you can then punish for not only stealing but for lying. if it's your visitor or whoever else...you can take the necessary actions.

good luck.