when I marry a Mexican citizen will she lose her B1B2 Visa?

The question to a Customs and Border Patrol agent is whether your wife has an intention to only visit with you in the US and go back to Mexico, or whether she intends to resettle in the US. If the latter and you are a US citizen or permanent resident, you should sponsor her directly for the green card. If she only intends to visit and go back, she may be able to convince the CBP officer that her B1/B2 visa is proper for her travels. Please note that the B1/B2 is not for her to spend most of the time in the US and only take occasional trips back to Mexico. That would be an abuse of the nonimmigrant visa. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.