I know that she can stay for up to 90 days but we want her to sta forever. She will quit her ob with this visit and I want to keep her here with me.

Marrying her here will not make her able to stay here any longer. She will need a Visa to stay. My fiance's dad married a woman in Thailand, and afterwards moved back here to the U.S. It took months for her to get a Visa, and she can only stay for 9 months.