I just wanted to chime in with my support. This will only be an issue for those clients who want a doula who did everything they want/plan to do (and luckily, I don't think this is the typical client).
A good response, and something to think about yourself is, really, it won't matter, because this is not about YOU, it is about the woman you are supporting. You don't bring your baggage, expectations, hopes for the birth, etc., that are personal and unique to you, with you when you support a woman. You are there to support her unique labor and birth.
If a potential client asked or said something to you about the fact that you haven't had a vaginal birth, it can be very satisfying for the person to hear you say, "Actually, my own experience doesn't matter here -- this is your experience, and I am here to support you during your unique experienc of labor and birth." It helpe to point out by not holding her to your own yardstick, she has more freedom to create and participate in her own experience.
Another aspect to point out -- we educate ourselves. We try to learn all we can and empower ourselves with knowledge. We make informed decisions, we do all we can, but there still aren't things we can control. The pelvis, the power, and the passenger have to work together. If you take the steps beforehand of educationg yourself, planning, and preparing, you can truly have the peace that your body or your baby knew things needed to be different. And that, my darling, has nothing to do with failing and everything to do with having a successful experience. (((((hugs))))))
It is normal to feel sad, regret, loss of the experience. The body knows how to protect herself and her young, and I firmly believe that. Sharing and teaching that principle, I think, can help not only open eyes, but it can also help heal.