it is difficult to ride with slower riders -- almost as difficult as riding with riders twice as fast as you! so, if her pace and/or style of riding is difficult to keep, you may need to limit your rides with her. as you ride more alone, keep an eye out for other riders and ask your LBS if they can recommend people or places where you could group-up with more riders ... in time, as your fitness and comfort level increases, so will your circle of riding partners!

personally, I have friends who are slower than me and ones faster -- both ends fun to ride with, but NOT all the time. it is nice to have variety!!!