Payroll Mapping

I use Quickbooks online and I'm trying to pay an employee for doing field work. I cannot find where to map this to a separate line in my budget. Her monthly salary is mapped to come out of her salary line. I need to have the field work come out of the "field work" line item in the budget. I tried to set her up a 2 separate employees; however, Quickbooks doesn't allow me to use her social security number twice.