Per the NPC Unanimous Agreements
VI. College Panhellenic Association Agreements
3. Preferential Bidding
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. If a potential member does not receive a bid under the preference system, she is eligible for COB.
The best and most accurate answer would be from your regional NPC advisor. You can find out who that is on the NPC site:
www.npcwomen.org