I have put together a synopsis and the first chapter of an autobiography for a friend - essentially, I would act as a ghost writer. My question is: if the subject matter is good enough, would an agent see past my poor writing skills and come back with 'Great idea, but you suck at writing, friend, we will use our own ghost writer', or would they just reject on the basis of my writing not being up to standard? Obviously, I wouldn't want to jeopardise my friend's chance at getting her story published.
If the story is really strong and we don't like the writing, we may indeed express interest in the story and want to talk about how the writing could be improved. But the story would need to be very strong, and different to what's already out there.
However, I'm more intrigued by the fact that you think you may jeopardise your friend's chances: I suspect your friend has either asked you to help or has agreed to accept your help knowing full well what your skills are. But if you don't believe in your writing, it's unlikely anyone else will. So put those shoulders back, then put one of them to the wheel and keep writing.