@Ksenia0
Unfortunately too many guests assume it's ok they just invite somebody over and let them crash. It's not ok in a hotel if they're not registered, and it's certainly not ok in a private home.
You don't mention anything in your house rules, so won't be able to say in her review that she had difficulties following them, but you could say something like: She was very friendly and blabla. As a guest new to the Airbnb system she probably did not realise that it was extremely inappropriate bringing in her boyfriend for a night into this private residence as unpaid and unannounced extra guest. I'm sure that with more practice and experience she will be an outstanding guest.
If you don't explicitly mention it in your house rules (the reason why so many hosts do!) a lot of guests will take it for granted that inviting somebody to see their accommodation and more is acceptable.
Your house rules are like the laws of your kingdom. What situation can you think of that you would not want to tolerate? Formulate that in no uncertain terms. No unregistered extra guests or outside visitors allowed. No smoking in the apartment, but it is tolerated on the balcony.
And so forth.