The Crayon Messages by Christine Thackeray

From the back cover:

Cath Reed has been feeling desperately lonely. With a husband away, a daughter on the brink and adjusting to her new ward, she hopes her new visiting teaching route will bring much needed companionship.

Then she finds out she has been given the hardest visiting teaching route ever. At least her companion Gwen seemed nice, an older woman in a nursing home who said no one had visited her in years.

Using this to her advantage, Cath calls her new sisters and convinces them to ...