I felt the same way, I thought maybe she got a disease like Arthur, or maybe she committed suicide, it is really annoying how they don't say.

ive speculated this before but i could see her passing from TB but taking longer to do so than Arthur.

I think she either died from suicide but more likely a disease

Sickness, most likely

I thought the game itself said somewhere that she died from tuberculosis? Maybe not

No, it's not said as far as I know.

Grieving and depression weaken the immune system, so I'd say it was probably a disease. Not necessarily TB, though. Cancer is also possible.

A death from a broken heart is a real thing, and I think that's what killed Abigail.

Probably of age, jack is pretty old when you play as him

He’s 19, as it’s only 3 years later. Abigail died aged around 37. Certainly not old age.

@Wagwan piffting23 most women died 30 years old back in those days, 37 is a very lucky age

30 would've been below average, I'm sure. Regardless, no one ever would've died of old age in their 30s. Life expectancy was low in the past because of people dying of other things first, not because they aged so fast they died of old age young.