@Nicola444
Sorry this happened. It happens to all hosts.
You have 2 issues, one financial and one is safety.
Because you are not comfortable with the stranger, you must ask him to leave or kick them out.
It requires diplomacy, cuz your guest may become defensive.
If you are comfortable with the guest's friend, you can ask for your extra guest charge.
If she doesn't pay, you must ask him to leave or kick them out.
The sooner you confront the issue, the better.
(Because I'm a man and a laissez-faire host, I'd let the last 2 nights of a 7 day reservation slide. it would bother me a little, but a 7 day reservation pays a lot of money...)