Another possibility for locks are combination locks. This means you can ask for the combination if needed. You could also have a spare key secured somewhere - somewhere you can get to it easily but may not be nice to retrieve (in a bucket filled with horrible slime, for example).

What would be ideal would be a combination lock which could be set remotely. So you ring your Mistress, get the code to open the lock, open it. Then, when she tells you to put it back on, it randomises the code and sends her a message telling her what it is. Shame that tech doesn't exist yet.