[AZ-AlphaXi]

Here's what the "Green Book" says about snap bidding

<Start Quote>
Snap Bidding
Snap Bidding is an option available to chapters which did not fill formal membership recruitment Quota spaces in bid-matching, whether matching by hand or by computer. Snap Bidding is not intended to fill spaces in the chapter Total. Snap Bidding is limited to any woman who participated in the designated formal membership recruitment.

Snap Bidding should be under the direction of the Collegel Panhellenic Membership Recruitment Committee, working with the chapters who have Quota vacancies. A signed Membership Recruitment Acceptance shall be filed with the College Panhellenic before a woman who has accepted a Snap Bid may be pledged. Snap Bidding shall begin immediately after bid matching and end with the distribution of bids, at which time Continuous Open Bidding shall begin.
<End Quote>

My understanding is that while a women who intentionally single preferences (SIP) is not eligible for quota addition, she is eligible to receive a snap bid. Although this begs the question of "she will accept it?" ... if she was so set on one chapter that she SIP'ed, she probably won't accept a snap bid from another chapter.