Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
The tax she would owe is dependent on a number of factors which you will need to provide for us to do the tax calculation.
First what will her income be on the bond and from other sources?
Is she single? What filing status will she be using?
Will she be itemizing deductions? If so how much?