I think you are blowing it out of proportion. You come from completely different cultures and you both need to respect that. You cannot expect your elder to come in and tell them how it's going to be or else. That's just not how it works in other countries. My house, my rules isn't African at all.
It is true a village is a family. I haven't been to Nigeria but I have lived in African villages before. If someone was ill or family less the whole village supported them. Fed them kept them clean. There was no MY home. If you are family you were never asked to leave and never expected anything from. Grandmas were not the care takers per se. Grandmas were taken care of. All the women of the village pitched in to get water to help out. There just wasn't this I don't know American way. Honestly I loved it.
Also all "women" over the age of 12 were called "mother" (meme). If you could have children you got this title whether or not you had children. It's like saying Sir or Ma'm I suppose in the US. It's respectful. I would say hello to strangers and use the term mother as a sign of respect not disrespect. I liked that also. Same with grandma (kuku).
There is also a big difference in smacking a child and threatening to do so which I think may be a cultural thing also. maybe in American when a white person says it a hand goes flying but not in other cultures. Usually the threat alone is enough to stop a child. No I don't do that. I am just putting it out there.
I think perhaps you should read up on Nigerian culture and find a way to respect different cultures. It's not about right and wrong.
BTW, the travel from Africa to America is brutal. I would be staying 6 weeks also! granted Nigeria is closer than where I went but maaaaaan is it a flight! If you're going to spend 2 grand and days on a plane I sure as heck would make my time worth it as most likely a return trip isn't coming any time soon.
It might be worth it for you to visit her. Learn and feel the culture. You can only learn so much by reading. You might want to google "culture shock". You need to understand she is NOT American and is FAR from it. Our culture is very I'm not sure how to word it. For example when I explained Americans have this like invisible bubble and people are not allowed in it my African friends burst out laughing thinking we were absolutely moronic. They also make fun of american black gangs. Where *I* lived people got CLOSE (which led to my bubble explanation as it made me uncomfortable). I mean strange men would touch my chest with a flat palm just talking. It wasn't sexual just they don't have these physical boundaries and don't get it just like we don't get how they COULDN't.
It's a little hard to explain.
I would not think she was rude and I would not confront someone like that. you can teach how Americans in general do things or how they think and she can try to absorb it but I think demanding your way or the highway isn't right either. But in the end you gotta do what you gotta do for your own sanity. Just my opinion.