Analyze the relationship between 'Gail Kelly' and 'Westpac' within the context of the input sentence.
Options: platform, legal form, subsidiary, employer

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