If she's a yearling, why not go ahead and buy her a 20-gallon-long right now and not ever have to worry about changing her home in the future?
I currently have three 2-year-old 3-foot-long snakes each in their own 10 gallon tanks, but these snakes are severely cramped and I need to move them into larger cages, asap. The only thing keeping me from moving them is I have no rack to put them in at the moment (still building it). They are making due, but it's definitely not ideal.