Now that's an unusual situation. I'd code a 59510-22 (assuming you are billing a global). Try to get extra reimbursement for the extra time, effort, and risk. You might be able to make an argument for one of the VBAC global OB codes if the patient started out as a VBAC, went to C/S, and then back to vaginal birth, but if she didn't start out as a VBAC, I don't think those codes fit.
As far as dx codes go, again there are no codes for "unsuccessful c-section converted to vaginal," so just code for each problem as it stands. You'll have to send an op report and cover letter to go with the -22 anyway, so everything should be explained in there.
At least that's all I can think of. Maybe somebody else has run across this situation before & has a better answer.
Becky, CPC