2. 15.3% of social security and medicare tax you have to pay - you are supposely withhold 7.65% from her paycheck, but this depends on how you negotiate with her. You might also need to pay Federal unemployment insurance tax depending on which state you are in.
3. If she needs you to withhold her Federal or state income tax, you can withhold and pay to IRS and State
4. You probably also need to file state quarterly payroll report to pay State Unemployment Tax. Check with state.
5. For your tax return purpose, make sure you have her SSN#