What did Ella's Mother (spoilers)

She died of deus ex machina

___
Anyone who has ever read any spoilers,
knows that Winter Is Coming

Drug overdose.

Corsets.

[deleted]

Hydrogen peroxide and artificial tanner. Perhaps if Ella avoids taking up the tanning habit, she will be lucky enough to make it to 40.

Breast cancer.

Seriously - tuberculosis seems like a likely candidate. She seemed to have problems breathing, and that disease used to be a rather common cause of early deaths before the age of antibiotics. And at least half of the women who die in novels written before the 20th century seem to die of it... (I guess because that allows them to die beautiful, that disease may make the sufferer pale, thin and weak but does not give them pustules or anything else unpleasant to look at).