That's a good point. The answer's completely inadequate and the letter itself is so vague that it's impossible to give any advice about what LW or anyone else "should" do, but at least it's unavoidably true that the two adult brothers are responsible for their relationship and nothing she can do can change that.

I'm with you on the real answer, with the addition that even if she can't or won't do therapy, in addition to accepting that it's up to them she should in general just seek advice from people she can actually describe the situation to, as melannen says above.