Shorter answer: in their home, usually a household employee. In your home or rotating, almost always an independent contractor.
Estimated tax payments are due 4 times a year starting on April 15. The payments can be made electronically on IRS and state tax web sites. The amount of payment can be calculated using various tax estimating programs. Roughly speaking, it will be 25% federal for most people, plus 15% self-employment if she is not a household employee. turbotax does not calculate estimated payments, it's only designed for end of year tax filing. Quickbooks or the Quickbooks self-employment bundle (which includes Quickbooks and turbotax) can do estimated payments if she wants to use Quickbooks to track self employment income and expenses (probably overkill if this is her only job.)
