It really isn't your place to try to educate her. And, if you try and she's reluctant, all you'll manage to do is destroy your friendship. If you have personally had a c-section, maybe you could discuss with her your personal experiences, but otherwise, just stay out of it. It's her body, her choice, regardless of how informed or misinformed she may be.
I don't really mean to sound so harsh...
What I'm driving at is that it is her own responsibility to educate and inform herself. Perhaps you could hint to her that maybe she needs to do some homework on the risks involved before she makes such a major decision. Then, if she asks for help finding info, you can point her in the right direction.
From my own personal experience, there was nothing worse than all those people who thought they should educate me on the risks of attempting VBAC. I see this in the same light.