Deductions & credits

The problem might be because you may have reported that your wife is not a US citizen or resident alien. She is a resident alien for tax reporting purposes since you made the election to have her treated as a resident alien.  

if you answered this question correctly stating she is not a US citizen but a resident alien, then there are other questions that appear that follow. As an FYI, I have included a screenshot of this extremely important question.

1. First if there was a income tax treaty, here you would say yes.
2. Then there is a question that asks if she qualifies for the Physical Presence Test or Bonafide Presence Test. Select these two links that explains what they are.
3. Then it asks for the 12-month qualifying period in accordance to the choice you made in the second step.
4. Then you would indicate the UK is her tax home.
5. Then it asks for trips abroad, indicating if whether or not she visited you in the US.
6. If these questions are answered correctly, your wife will qualify for the foreign income exclusion and a Form 2555 willk be added to your return.