Wow, this is a really hot-button issue. I can try to understand your point EH, but I think you are wrong about one specific thing. Being older DOES sometimes give people a pass in regards to many things. Being very, very young ALSO gives some children a pass on their behavior some of the time, but one would hope their parents are teaching them better manners and menschlechkeit.
I think you were mistaken in making the mountain out of this story, when your daughter and you could have moved over one seat to accommodate an older woman. Instead, you showed your daughter how two women can bully each other. SHUL is not the place to prove you are right.
Binayeseirah answered you very well. And so did Aries.
I have to say I am very much surprised that on a forum that is constantly ragging on the lack of tznius as the cause of all the ills of the world, that so many of the posters here don’t seem to recognize that it is the lack of menschlechkeit is the main problem. Whether or not the older woman was right is not the issue. The issue is how EH reacted to her and worse, what she did with her daughter. And the fact that ANYONE here has defended what prompted that action, really shocks me. What do we get with an “I’ll show HER!” attitude? We are supposed to be better than that. If someone acts like a bulvan, there are only a few circumstances where one should not be mevater. Acting out in front of one’s child is not the best way to solve a problem. And coming to shul an hour and half early on Shabbos, in order to get a seat for something going on AFTER Shabbos, is also not 100% the right thing to do, especially if you are using that as the excuse that the seat was saved for the child who was sitting there for that length of time prior to the leining.
In any case, I can understand EH feeling the way she did, but I think the situation could have been handled differently, and in this particular case, given there was another space for her daughter to sit, it would have been better in this instance not to make a spectacle in shul.