how do houses select candidates during COB?

my sister is currently going through spring COB and we're both trying to navigate what COB is like. i never rushed sororities in my time at purdue, so i really don't know how to help her (senior now). we've only ever heard of formal recruitment. some houses have more formal events, while one house privately messaged her for a one on one recruitment date with a sister. are they going to determine who gets a bid based off of a single coffee date? what is the COB selection process really like?