@Robin1427 Of course she can do that. It is the host's property and she gets to make the rules.
Most hosts do not allow visitors of any kind. Why? Because guests abuse the privilege. Suddenly a visitor turns into an overnight guest that they are not paying for, or that puts them over capacity. Visitors can also mean parties. While your intentions may be good, you have to remember that not all guests are responsible or respectful of a property during their stay.
You are a guest, and that doesn't give you privileges that you would have in your own home. I don't know what this host has in her property description and house rules, but I do hope you reviewed everything carefully before booking, and/or asked BEFORE booking if you could have guests. If not, I'm afraid you're at her mercy.
If the family and friends are local to where you're staying, perhaps you could pick a different place to gather.