It is visa fraud if she plans to enter the US , marry and adjust her status. If you marry in the USA , she has to stay only for the remainder of her permitted stay (determined by CBP at point of entry, its usually 6 months) then return to Europe petition for her to move to USA. If you marry in Europe then you go back to USA ALONE then petition for her to move to the USA. Green card petitions are slower, however if you become a citizen...you can upgrade your petition and it moves faster.