from. In addition, withholding is deemed taken out evenly throughout the year, regardless of when it's actually withheld, as opposed to estimated payments, which are credited to the quarter in which they're actually withheld. If you're underpaid YTD, you can make it up with payroll withholding and avoid penalty.
Without knowing your exact situation, I would say generally it would be more convenient to have your withholding adjusted to cover you both.
As an aside, your comment regarding her inability to have taxes withheld raises a question as to whether she's deemed self-employed. If so, you'll have to also factor in FICA and Medicare, a real treat.
Standard disclaimer that this advice is not a substitute for professional tax advice.
Edit to add that cdb9396 makes an excellent point regarding divorce. But in that unfortunate event, she'll be the one with a tax problem...not you.