You should file as Married filing Jointly (MFJ). Although she doesn't have enough income to file on her own, her income must be included on your MFJ return.
There is no such thing as a "Marriage credit". You are also not allowed to claim a spouse as a dependent. But using the MFJ filing status gets you lower tax rates and a bigger standard deduction (twice the amount of a Single or Married Filing separately [MFS] standard deduction).
You may be tempted to file MFS, so that you don't have to include her income. Don't do it. None of her income will effectively be taxed, even though it has to be reported on a MFJ return. The bigger standard deduction wipes out all her income and some of your income too.
