:welcome:
once you are married, if you want to live here she can apply for a family resident visa here in Spain at the nearest extranjería to where you live - if you have a search of the forum there are discussions about this process - start with the 'useful links' thread which is 'stuck' at the top of the page
as far as getting married in the US I have no idea - maybe ask here America Expat Forum for Expats Living in America - Expat Forum For Expats, For Moving Overseas And For Jobs Abroad