Bringing someone along

Hi all

I am hoping to get a date soon for my assessment, but i understand that ill be asked to bring someone along who has known me for a long time. I plan to bring my older sister.  My question is though, would she be with me all the time im being assessed?  I would rather that not happen, i dont mind her being asked questions separately, but id much rather be interviewed on my own, just wondered what the standard is?