Well your friend had an obligation to clear this with her parents beforehand.

The age of you and friend might have something to do with this. When my children were teenagers and young adults this happened frequently where someone else unexpectedly stayed for dinner. Beyond their early 20s though this was a definite no-no which I did not appreciate.

I want to add another thought to this. If you feel as though you are putting these people out then I think you ought to be making use of yourself. Offer to help. Set or bus the table. Help with dishes and the clean-up. Is there any way to help with meal preparation? Call me strict but I have an expectation that people offer to do so when visiting me. I don't always take them up on it but it is my expectation they recognise the work involved and make an offer to help.