Make the exit so slow that it doesn't feel like a break-up for either of you. People usually respond best to things they figure out for themselves, which gives them a sense of control, rather than having someone tell them they are doing something. Spend just a little less time on the phone, in person and closeness each week. You recognize that she is not whats best for you right now, thats good you see that, as that means your not whats best for her right now either, but you can still be a great support to her. It also doesn't mean you can't be a good friend to her over the longer term. Her getting some help with how she feels is critical though as it looks like you might do exactly what she fears most, just walk out. Can you stay around a little longer if she gets help and makes progress?