Imo, she has been lucky. The Carrier Information Guide specifically states: "Expired Conditional Resident Card, Form I-551 accompanied by Original Form I-797, Notice of Action indicating the card validity is extended". The guide is not a USCIS document.
"The U.S. Customs and Border Protection (CBP) Carrier Information Guide serves as a reference aid for travel industry personnel. It outlines the required documents that apply to persons entering or departing the United States. Carrier personnel are urged to familiarize themselves with all sections of the publication and reference it in their examination of travel documents."
My point is that, regardless of what USCIS says, there is a possibility she will be denied boarding. Good luck on the rest of your immigration journey. Next action for your spouse is either an I-751 interview or N-400 submission.