Good afternoon and thank you for submitting your question. My name is Alexander; I'm an EA and am happy to assist you with this issue.
As I understand your question, you want to know whether you may owe additional tax, after the 20% withholdings from your wife's 401(k) distribution. In this case, as your wife was 59 1/2 at the time of the distribution, there are no penalties to consider, so the withholding would be strictly for Federal income tax. Depending on the other items of income and deductions (wages, interest & dividends, capital gains, rental income, etc. and the amount of itemized deductions or standard deduction claimed), there could be additional tax due. If you compare your taxable income from 2014 to your expected taxable income for 2015, you should have an idea of whether any additional tax will be due.
While the nature of your question doesn't lend itself to definitive answers, the best answer to your question is: yes, it is possible you'll owe more when you prepare your 2015 tax returns; however, it is largely dependent on the rest of your income/deductions.
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