Did the person who told you to expect to pay a lot not tell you how much to expect to pay? Sounds like it may not be too complicated, so I would just gather the info and call the guy above. If you think it's complicated, call a bigger firm and expect to pay more. The penalties are ticking up the longer you don't pay, so I'd get it figured out asap and then adjust withholding accordingly for your pay to cover her tax in the earlier part of 2024. Talk to whatever CPA you hire to confirm they understand the presumption of timing of withholding payments for penalty purposes.