do local sororities underground?

First rule about undergrounding, don’t talk about undergrounding

No, local sororities don't underground. Probably due to the fact that they all want to get each other in trouble in one way or another, so if another sorority found out they'd be screwed. The closest thing to undergrounding that you'll get is someone "guaranteeing" you a bid for the next semester or whenever you're eligible. But still there's not way to really guarantee anything.

Its not typical for sororities to underground in general because the stakes are high if they get caught. Frats do it a lot more frequently. If a sorority does underground they probably won't make it well known to the public that they're planning to.

No sorority undergrounds. It is a known thing. You can get deferred to when you do have the GPA, but you will not pledge and become a member until you have the GPA!
But don't be upset about it, if girls like you enough they will keep inviting you out until you can finally join!