Take context from the input text and decide on the accurate relationship between 'Gail Kelly' and 'Westpac' from the options provided.
Options: legal form, subsidiary, employer, platform

Nic Walker Share on twitter by Sue Mitchell South African retailer Woolworths Holdings has turned to former Westpac chief executive Gail Kelly to help transform itself into a leading southern hemisphere retailer after last year's $2.1 billion acquisition of David Jones.
employer