You can get married right now, the longer you are in a relationship the easier it is for you to get your green card. But dont file your paperwork for adjustment of status. Wait till she gets her citizenship and the very next day you could file your paper work. You would get you green card within 2 years.  But if  you are trying to base this relationship just for green card then i would say you should think and rethink about it. These types of marriage dont last long. I've seen it all the way. If you are really certain that she is the one that you want to spend the rest of your life then congratulation and move forward. So for now just get a marriage certificate take few pictures while getting married etc etc. Later it would be easy for you to convince the interviewer that you didnt get married seeking benifits.

God bless you
YekloYatri