Also, I don't think anyone actually explicitly stated "it's selfish of her to buy a horse for herself instead of party clothes for the children"

Pretty near, though. On this thread:

Perhaps I should have reworded that to say Was it reasonable to spend so much on herself when some of her children are going without some things? link (http://www.livejournal.com/community/trennels/3795.html?thread=63699#t63699)

and by "some things" you explicitly said in the same comment

But on the other hand, it seems like she's spending money on something pretty frivolous when some of her children don't even get new best clothes

So yes, this "got interpreted" as "New party clothes for all is more important than Mrs. Marlow!" because that is precisely what it appeared to be you were saying.