Wife is switching to being 1099 rather than working as an employee - can we get away with withholding her expected taxes from my paycheck or do we need to pay quarterly?

[DanPaul02]

You can withhold her taxes from your earnings.  You may need to file a new W4 to be sure that enough is being withheld to cover her taxes, social security, and Medicare when you file jointly.

[fanfare]

Since the SE tax is 15% right off the bat, do you want your take home pay to go way down to cover this and her income tax?

No, better to make estimated tax payments from her income.