Hi I'm a natural born citizen and I want to marry my fiancé who comes to the states legally with a visa every couple months. I want her to get her papers so she could stay here permanently and we could start a family because through her visa she has to return every couple of months which is a bummer. I live in Virginia and I guess my question is how to go about marrying her so she can get her papers and if so would the process be faster because she is here legally and.. Would it be better for me to go to El Salvador and marry her there or for us to get married here in Virginia... please help I love this girl and can't stand seeing her go back to her country every couple of months. Thank you

Actually she does not have to go back to her country, just leave the US and re-enter.

Does not matter where you marry, does not give her any special rights, she should apply for new visa to allow her to marry, If not, after marry, she applies for a change

You could apply for a fiancé visa (K1).
Nonimmigrant Visa for a Fiancé(e) (K-1)

The key is how she entered US.. you can get married and file for change of status. K-1 visa does not apply in this case.