Never have played this game, so honestly don't really know what's going on, but I like to think that the reason Edith Finch died in childbirth is because her parents wanted to delay her birthing date because they wanted her to be married beforehand. Idk, it says she has a wedding band in her article.
Maybe they thought it would be better if she was 18 (I think the wiki said she turned 18 soon after giving birth) because there are a lot of risks with underage pregnancy, but ironically delaying your birthing date also comes with risks.