She was denied for immigrant intent.
If she is properly petitioned for an immigrant visa, that will not be an issue.
However, you DO need to get your documents in order. Nigeria is notorious for fake documents. And contrary to what your lawyer recommended, the party line here on VJ is generally not to do a DNA test until the request comes from NVC or (more likely), the embassy. Embassies use particular DNA labs, and they will reject results from unauthorized sources.