So - this is interesting, folks... Directly from the Unanimous Agreements:
4. A signed membership recruitment acceptance or a continuous open bidding (COB) acceptance is binding. If a potential member receives a bid under the preference system, she is ineligible to be pledged to any other NPC fraternity on the same campus for one calendar year.
But then we have
8. If through the primary recruitment process a potential member accepts a bid and then has her pledge broken by an NPC fraternity or breaks her pledge, then she is ineligible to be pledged to another NPC fraternity on the same campus until the beginning of the next year’s primary membership recruitment period.
So which is it, Recruitment/NPC experts? To me, the scenario described by the OP fits #8, not #4. She accepted a bid, pledged, and then broke her pledge.
UNLESS, of course, the OP is talking about locals, or non-NPC sororities (of which there are many, many, many). Then it would be a different matter entirely.
One last thing:
Why ask the Greek Life office? It's the NPC MRABA that applies here. Greek Life has been known to make mistakes. I'd check with the NPC.