The Yangebup woman�s mum died in 2003 after a battle with pancreatic cancer.
Twelve years on Ms Johnson will be among the thousands taking part in the HBF Run for a Reason this Sunday.
So far she has raised more than $500, which she will donate to the Cancer Council WA.
She had set a target of $200.
Ms Johnson said she now felt strong enough to give something back.
But a personal mission to lose weight and get fit has helped, too.
�It�s taken a while for me to reach that point where I can help others, but it�s my turn to give something back,� she said.
�I can�t wait to do my mum proud and am so excited to have raised so much money and hopefully I can raise some more. I�ve been overwhelmed by the support shown.�