I must confess I read the book sometime ago, but I forget the cause of Rose's death. Was she ill?
While I am asking, what were the political conditions in that part of Ireland then? Was there fighting with the English, IRA bombings, etc? From the film it seemed a peaceful environment and not poverty-stricken, as we have been led to believe from books like ANGELA'S ASHES. Eilish's home, though modest, was pleasant and no-one was starving.
Enniscorthy is in the southeastern part of Ireland; it had nothing to do with the "troubles." It was peaceful but had limited opportunities for all the young people. I don't think it's much different from any small town or rural community people have to leave in order to have a life for themselves. By moving to Brooklyn Eilis was able to get a job, obtain a sponsor (the priest) and have a free education. The movie pretends that a parishioner underwrote Eilis's education but Brooklyn College was actually free back then. Ireland had been cut off from World War II, wasn't part of the Marshall Plan, and was very rural. NYC was booming, had an Irish mayor and cardinal, and was welcoming to English-speaking Irish women who wanted careers in nursing and teaching and expanded opportunities from there.
Frank McCourt came from an enormous family in Ireland with a lot of alcoholism. The size of the family and the alcoholism and depression in his family contributed to desperate times. Also, bear in mind he exaggerated and embellished. When not teaching at Styvesant Highschool in NYC he was often upstairs at the Ensemble Studio Theatre or Irish Arts, writing away. His books are just as much about the stuff he totally made up as they are about real things. He always wished he could be his brother, McCauley (who became an actor).
A friend of mine knew him well.
Rose's death was written off as heart ailment in the book as well as the movie. Re-watching the movie, you can infer a subtext that the actress is playing - that she knows she's ill and is setting up her little sister for success before it's too late. She's getting her little sister away from the mother, and she gets choked up when Eilis says "I'll come to visit, won't I?" because Rose knows it's unlikely they'll see each other again. She expects to die before Eilis can visit. I think the performance justifies that interpretation.
I think Angela's Ashes was set earlier in the 1930s or 40s and is about a completely different class. In Brooklyn the family looked as if they were comfortable, maybe before the father's death. Rose is educated and plays golf but Eilis couldn't afford much in the way of clothes or further education. The Irish economy was stagnant until the late 1950s due to protectionism which limited foreign companies opening. There was huge emigration at this time. Despite not being involved in the WW2 Ireland did receive Marshall aid which helped with economic recovery in the 1960s and 70s. I'd recommend trying to get a copy of the film Older than Ireland which was released this year if you are interested in the social history of Ireland.
I loved "Angela's Ashes" and "'Tis" but by the time he wrote "Teacher Man', meh. A friend told me he angered a lot of people at home but I would guess that's expected.