You answered elsewhere that you are in Washington, a community property state.  If you want to disregard community property laws and therefore, disregard tax law, you can probably get away with that.  IRS doesn't go down many of those rabbit holes.  But the correct procedure would be to determine when the community was split (this varies from state to state) and then estimate income and withholding for the wife, up until that date.  And of course, share with her what she needs to comply with the law.  (Not that it matters, but are there kids involved?)