You need to make sure you have your finanicial situation sorted via bank statements for yourself or both of you showing regular income and if at all possible savings but deff a regualr income that would support both of you.
Also proof of seeing each other and staying with each other, proof of accomadation that you have in the UK and proof she can live with you there, so letter from landlord and proof of rent, letter off your employer giving employment details how much you earn is your job perm, bills with your address on and name.
If it is straight forward and you have all your financial proof it would not take to long for her to send everything off and most people have been approved in a few weeks or so, there may be some that have taken longer.
But you need to make sure you have all your paper work together.
You can go and get married over there on the VWP we did, and my wife and I stayed for a month to see my family and friends and a honeymoon.
Good luck I hope some of this will help get you started on the right path. Also think about where your going to be living what area of the UK and budget for the bills rent ect.
Again good luck.
Indy and wife