In the book she dies in child birth because she takes a drug to bring on the pregnancy early, so Warleggan will stop having doubts about Ross's child that she had. But she's addicted to this drug in the show, so I was saying it wouldn't surprise me if she dies because of this sleeping drug.

She gets pregnant again in book 6 I think (which will be next series because they're doing two books to a series) and this time it's by Warleggan. However, there's a big rift in their relationship because he knows it's Ross's child, so to convince him she's prone to early labour she takes a drug to bring the pregnancy on early. The drug kills her in childbirth. Dwight knows about the drug, but keeps her secret. Warleggan is then convinced and then raises both children as his in respect for Elizabeth. The next book skips to the next generation. So to Warleggans children and Ross's. The main characters now basically get pushed to the sidelines.