How about this? What if you can somehow get her to go to a location outside the house, and the person who answers the door acts like the party is happening somewhere else?
assitant
What would you do if you were going to surprise her?
assistant
I need to plan a surprise birthday party. Can you give me some tips?
user
Sure! How about you have a family or group discussion about what sort of things you all want to do at the party, and I’ll write down the ideas you all come up with? Then I can help you choose a date, make a final guest list, and put all of those things into an email for you to send to the guests?
assistant
Okay, well I have the date picked out. But I need to know how to keep it a surprise from my friend.
user
What do you want the party to be like?
assistant
Well, it is a surprise birthday party for my friend. How do I keep it a surprise and get her to the party without her knowing?
user