As Eilis' Irish landlady, Mrs. Kehoe is perfectly situated on the border between Ireland and America (metaphorically speaking, of course), which leads to quite a few complications in Eilis' life.
Oddly, what bothers Eilis most is how much Mrs. Kehoe seems to love her. Mrs. Kehoe frequently gives her preferential treatment, which "carried with it the firm idea that she and Eilis stood apart from the other lodgers" (3.35). This drives poor Eilis crazy, evoking memories of her former boss Miss Kelly's condescending attitude towards people of lower classes.
Because of this, it's only fitting that Eilis' expulsion from Ireland is brought about by these two women, with Mrs. Kehoe telling Miss Kelly about Eilis' marriage to Tony. Although this basically forces Eilis' hand, it also reminds her why she left Ireland in the first place.