Why does Vera think she has been asked to come to the island?

In the book "And Then There Were None," Vera Claythorne,
who was a young and attractive teacher was hired through a letter from Una Nancy Owen
for a short stint as a secretary.

She was actually called
on to the island to punish her for the crime of killing a young boy in her care named
Cyril Hamilton. Her cruel and selfish nature made her allow the boy to swim too far into
the water, from where she knew he would not be able to return alive. This was in part to
do with Vera’s relation with Cyril’s uncle Hugo Hamilton whom she thought would be rich
and able to marry her if it weren't for the boy.