How do I get taxes already paid for my household employee refunded back to her?

We had an after-school nanny for part of last year. We thought we were going to pay her more than $2600 so we set up an account in SurePayroll and she (and I) had payroll taxes taken out automatically. However, we ended up only paying her around $2400 so I canceled the the SurePayroll account to do all the W2 information for myself. I was debating not even doing the W2 but because I wanted her to get the payroll taxes back that were already paid, I went to the Social Security Website to use their free W2 online form.

The problem is when I put in the wages at $2400, it's telling me to put $0 since it was less than $2600 but when I change that to $0, I get an error message because the money I entered into boxes 2, 4, and 6 are not $0. I called SurePayroll and they said they can't help. Any thoughts as to how to approach this? Thanks in advance.