I'm not a tax person, but I have always done my own so I'll give it a shot. It all depends what other assets she may have that will be taxable such as interest income, dividends, etc. If she has other taxable assets she may want to claim "0" and have the extra withholding to cover these at tax time. If she only has her regular income and files form 1040 E-Z, she could probably get away with claiming "1".