Since you filed a joint return last year, the AGI for each of you should be the same. However, your wife's SSN is not in the IRS system as being on a previous return, so enter zero for her AGI.
If you know the 5-digit signature ID (aka self-select PIN) you used to sign last year's return, you can use that in lieu of your AGI.
Please see this TurboTax Help article for more information:
TurboTax Online instructions for E-file reject IND-031-04 or IND-032-04: The AGI or Self-select PIN ...
