How can she stay here to have baby and will baby be US citizen if born in the US to a Guatemalan mother and dual Guatemalan/US citizens father?

The potential difficulty here is that the couple was married prior to her coming to the US and U.S.C.I.S. may think that she came to the US with the intention of never going back. On the other hand, good things in your friend's favor for arguing that she did not try to circumvent regular US immigration procedures of waiting overseas could be that she was not petitioned for permanent residence prior to coming to the country (if that is true) , an intervening event occurred that made her reluctant to go back home (the pregnancy), and if she had the 10 year visa previously and not just for this trip. (Kindly note that I assume that you mean that she has a B visa instead of a D visa. The latter type of visa is for crewman such as a flight attendant and such individuals are not eligible to adjust status in the U. S.) 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.