I agree with Thompson'sMommy that it's nobody else's business.
If you are in someone else's house and she wants to nurse, just slip off somewhere private together. Of course, I don't think you should "have" to be really private about it if you don't want to be.
But I just know, having had older nurslings myself, that sometimes it comes down to protecting my child from our weird society. Some people have the societal corn cob shoved so hard up their butts, that it's too tightly wedged to remove it unless it's something they really WANT to remove.
And most people just simply don't feel any need to question the biases that they were raised with. They're happy leaving the corncob right where it is, and they're so used to it, they can't even tell they're emotionally-constipated.
I think every mother-child pair will probably work this issue out differently. I know I liked helping to normalize child-led weaning, by being pretty open about nursing my daughters up until around age 3.
But then I got concerned about the ways that some people would make negative remarks in front of my children. And I've also heard some horror stories about kids getting taken from their mothers because Child Protective Services didn't feel it was normal for 4 or 5-year-olds to still be nursing.
So somewhere around age 3 with each one, we started slipping off to a private spot if they asked to nurse in a place where I didn't feel comfortable just whipping it out, because of the people we were with (not that I was scared of offending them -- more that I was concerned about how their negativity might harm my child).
It was fairly easy by this point, since by this age their main interest was in nursing to sleep or upon waking -- and occasionally during the day if it was a relaxed day at home. Away from home, they tended to be more interested in whatever activities we were doing and whatever people we were seeing, so it didn't even come up that much anyway.
If it did, we just slipped off for a few moments. I normally object to the idea of nursing in a bathroom -- but I did that sometimes with my girls when they were older nurslings. They usually just wanted to nurse for a few minutes, if at all, when we were out by that age anyway.