Life could do nothing for her, beyond giving time for a better preparation for death; and that was given. I saw her placed in comfortable lodgings, and under proper attendants; I visited her every day during the rest of her short life: I was with her in her last moments.”
In this time it may actually have been more important for a woman to marry a man who cared for her than to marry a man she cared for. Lacking either could be emotionally devastating, but the former lack could also end life itself.
The complicating factor here is that Eliza is the one who leaves her husband. She could have survived, presumably, in an unhappy marriage.
And there is not just one reason her marriage is unhappy. She lacks both a husband who cares for her and a husband she cares for.