Girls can't just attend each sororities event until they get a bid from one of them?

Certainly the wrong way to look at it. You can always decline an invitation if you decide a group is not a fit for you. Not to mention, what happens if you "think" you want the one recruiting last and they don't invite you??????

I can't imagine that NPC HQs would be okay with even the most informal of rushes as you've described it. Unless you're including groups that aren't NPC.

It is not the NPC way to make a girl choose in advance to rush one chapter over another. I would guess you are overlaying NPHC rules (because they DO expect you to choose in advance) or these are traditionally white but not actually NPC sororities.

And to put a finer point on it, screw what they expect you to do. I would rush at every possible chapter available to you so that you can make the most informed choice possible. You need to understand that while many girls make a sorority decision based on her college experience, most of us here have taken our lifetime commitment as just that. Flipping a coin about which parties you're going to attend for the next year and a half is not what joining a sorority should be about. At least it shouldn't be the only factor.

I don't know if this is the situation but at the school I went to, a large public institution, the chapters themselves decided whether they were going to have an informal rush in the spring. Most of the chapters are huge and are at chapter total and do not always participate in any type of informal or open rush activities. The chapters that do set their own schedules for parties so what OP is describing could very easily happen with one chapter holding parties one week and another later in the month. In this case the PNM would decide whether she wanted to attend the events for a particular group

Whether the chapters decide to recruit is not the issue. It's the idea that you have to pick one to visit and can't go to any others. That is NOT the NPC way and that's what we are discussing. She thinks she can only pick one group's parties to attend. If they don't give her a bid or invite her back to even a second party, then she's pretty much out of luck. Not the way NPC does it - more like NPHC or locals.