OP, like others have pointed, If i was the IO, i would be very puzzled as to why a couple who haven't seen each other in 3 years would have one of them in a neighbouring West African country, less than 2 hours flight apart, and not seize that time to see each other; a time span of almost 3 years with no physical presence with each other is bad already.
That said, i'll like to point you a glimpse of light at the end of the tunnel, which is the Interview officer telling you about the fraud department getting to you. They don't often let out that information, especially if they will be investigating the beneficiary-in my view, that would be counterproductive. They might just want to establish that your marriage is bonafide which i assume might involve checking the Petitioners past records with USCIS to establish a pattern since she's sponsored before or probably going to the petitioner's residence to confirm some things. But then, that's just an assumption, you should get ready for a potential visit from them too and even a stoke interview.
Secondly, I will STRONGLY suggest you avoid any steps that might look like you are forcing evidence out of the norm, that's more suspicious and might seem like someone covering their tracks, even if the motive is honest. If your wife work don't permit her to leave for a long time, it would be absurd for her to now take months off just to be with you, stick to the what's natural.
on a final note, if its possible that your wife can visit sooner, make an appearance at the Lagos Embassy, that will help your case. They have different departments for Citizens but its still within the same establishment. i wish you the best