I can't imagine walking out on a mum because she had an epidural.
To me that just screams of a doula who cannot keep her own stuff out of other people's births.
I've formed a connection with all the mum's I've worked with and the thought of walking out on any of them in labour - no matter what's happening - is just abhorrent to me. There is nothing she could choose that would make me entertain that for a second. Doulas are in it through thick and thin, I just can't fathom why you'd leave someone up the creek like that.
As far as pushing someone too far, that's such a fine line. It can be really hard to tell sometimes when a woman has really reached her limit or just needs more help. I think I'm getting better at this though!