Thanks for asking your question! I'm sorry to hear about your tax issue and I'm going to try my best to help you understand or resolve it.
In boxes 3 and 5, place $6,300. For box 4, take $6,300 and multiply it by 4.2% (in 2013 this value would be 6.2% but in 2012 it was 2% lower). For box 6, take $6,300 and multiply it by 1.45%. For box 1, add together boxes 3, 4, and 6. She will be taxed on the amount of taxes that you paid for her.
When filling out schedule H, you will use $6,300 as the wages subject to the various taxes.
A good step by step tutorial is available, HERE
Please let me know if you need further assistance. Thanks again for using JustAnswer.com and have a great day.
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You should be aware that your question, as with most tax questions, can never really be answered completely...addressing all the permutations; that is because of the many assumptions that have to be made I have done my best to determine what I think you are asking and answering it in the most direct and understandable manner possible. If, however, after reviewing the questions, you have any uncertainties or further questions, please do not hesitate to ask.