Isabella Charters Jardine was Lillie's aunt,
being the baby sister to William Jardine (Lillie's father).
According to these documents the following dates apply for her:
BIRTH: 27 March 1886,
Benlester, Lamlash, Isle of Arran, Scotland
DEATH: 23 August 1888,
Colquhar, Innerleithen, Peebleshire, Scotland
It appears she died from the effects of hydrocephalus and epilepsy (fluid on the brain) after suffering from it for at least a year.
She was nearly 2 1/2 years old when she died,
so William would have been about 5 years old when she passed away.
Birth Notice:
SOURCE: Southern Reporter (Selkirk, Scotland) 1886, Apr 1, p3,
via findmypast newspaper archive
Death record:
SOURCE: ScotlandsPeople.gov.uk
Death notice:
SOURCE: Southern Reporter (Selkirk Scotland) 1888, Aug 30, p3,
via findmypast newspaper archive
