Oh, do I have a story!!
When I pledged we started out with 4, we ended with 3.
There was this one girl named "J", she was a pain and a half. When we first all met (the first activity) we got to talk a bit. Well, that's when she informed the rest of us how much she hated the TKE's on campus. That was not smart seeing that I and another pledge sister are both Sweethearts of the fraternity. I mean...she bashed and bashed the guys...oh lord we hated her. Funny thing is that she only knew ONE of the guys...and she based her entire opinion about them due to him. (and he's not that bad of a guy either) Also, she thought that just because she hung out with them (the sisters) a bit more they would be easier on her. That got on everyone's nerves big time.
Thankfully there's a clause that if majority of your class dislikes another pledge sister you can blackball them yourselves.
We enacted that first thing.
She ended up leaving after that semester and quitting school..oh well! Oh..and she loved to skpi activities and blame us for stuff.
My other pledge sisters..well...I loved them the first time I seen 'em!!
ETA: The decision to blackball a fellow pledge sister is also in conjuction w/the actives. Basically the class goes to their pledge mom w/the problem pledge. They watch her a bit, etc. Then it can be enacted if they see fit. Also, pledge classes are around 2-5 people, not 20-50 like many of you have, so you -have- to get to know them 
So, if you let that one "problem person" in, they can be a problem once their active (sororities here are 5-15 in number).