I'm turning 21 tomorrow and plan to go to dinner with 11 of my closest friends. This dinner has been planned since last week and I made the reservation days ago. Also, all the guests were informed of the plans a week ago and all said they could go then. About an hour ago, one of my friends texted me saying that her older sister will be visiting her tomorrow. Her sister is either 26 or 27 and I have never met her. My friend asked me if she could come to my birthday dinner. 

I told her that the reservation had already been made days ago and the restaurant would not let me change it. This place has a policy that you have to make reservations for parties over 8. She replied asking if I could add one more because she feels bad that her sister is going to be in town and apparently wants to join us. She then offered to call the place herself. I told her sorry but repeated that they won't let me change it because I tried to add someone last night (a lie, but I just wanted her to give it up). I added that I think her sister would feel awkward among all the younger strangers. She replied that her sister wouldn't mind and said we'd "play it by ear."

I don't want to be rude but I don't want her sister coming; it's my birthday (my 21st too) and I only want people that I have invited. Her sister is also considerably older than everyone else and doesn't know any of my other friends. My friend knew about this dinner last week and told me she could go then. I don't know when the plans for her sister visiting came about but she should've taken everything into account when she made both of these plans. I'm worried she'll call the place and have them change the reservation or just show up with her sister at the dinner.
user
Friend wants to bring her sister to my 21st birthday
assistant
I'm turning 21 tomorrow and plan to go to dinner with 11 of my closest friends. This dinner has been planned since last week and I made the reservation days ago. Also, all the guests were informed of the plans a week ago and all said they could go then. About an hour ago, one of my friends texted me saying that her older sister will be visiting her tomorrow. Her sister is either 26 or 27 and I have never met her. My friend asked me if she could come to my birthday dinner. 

I told her that the reservation had already been made days ago and the restaurant would not let me change it. This place has a policy that you have to make reservations for parties over 8. She replied asking if I could add one more because she feels bad that her sister is going to be in town and apparently wants to join us. She then offered to call the place herself. I told her sorry but repeated that they won't let me change it because I tried to add someone last night (a lie, but I just wanted her to give it up). I added that I think her sister would feel awkward among all the younger strangers. She replied that her sister wouldn't mind and said we'd "play it by ear."

I don't want to be rude but I don't want her sister coming; it's my birthday (my 21st too) and I only want people that I have invited. Her sister is also considerably older than everyone else and doesn't know any of my other friends. My friend knew about this dinner last week and told me she could go then. I don't know when the plans for her sister visiting came about but she should've taken everything into account when she made both of these plans. I'm worried she'll call the place and have them change the reservation or just show up with her sister at the dinner.
user
I'm turning 21 tomorrow and plan to go to dinner
assistant