I do our taxes with TurboTax, complications and all, so I wouldn't have a clue about professional tax preparation fees.
My dad used to do his own taxes with pen and paper (old-fashioned forms), but he hired a tax accountant the first year he was retired since he also had some other complications. Now, a few years later, he files online (after doing it manually with pen and paper) and he has rental properties in a different state and other complications.
It sounds like this year's taxes are a done deal and you just have to figure out how to pay the accountant. Maybe she will take payments? Like some now and the rest when your return arrives? Or some now and the rest on 4/15? Or some other mutually agreeable plan.
For the future, perhaps you could plan to do them yourself? You'd have the previous years returns to look at for guidance and you can always call the IRS for free help. The phone lines are easy to get through in January/February and get busier and busier as April 15 approaches.