you had to have booked seperately? well i guess you didnt have to but you would have had to get her the same day ticket you had, for instance everyone has the same 7 day hopper.
if she just leaves, she wont need to check out, youll check out when you leave.(im assuming you are all staying in the same room) then if you all had the same reservation and the same ticket, yes you will get her left over credits.