Based on my own experience with the various genealogy testing sites, your results can change over the years as they refine their methodologies. Mine sure did. The first time I did the analysis, I got some really odd results. My siblings and I were kind of scratching our heads over it. The results showed me to be roughly 70% of the ethnicity I expected and the other 30% was all over the place lol. Just some really odd results based on what we knew of our family history, though I understand that odd results are exactly what is often revealed by this testing. Origin stories that have been passed down are sometimes false or a cover up or "enhanced", to put it kindly.
I kind of shrugged about it and said, oh well, that's interesting, I'll have to look into these results at some point. A couple years later, I received an email from the site saying they've updated my results from their latest analysis improvements. I went and took a look and sure enough, the results were exactly in line with what my siblings and I had originally expected them to be. All the odd %'s were gone. Poof.
So, that was my long way of saying that MM's belief in her 43% Nigerian ancestry might be based on a faulty analysis from several years ago.