In a sales role, if you don't sell you get binned. That's just the way it is. Targets and priorities change every year, as do payment plans. If you don't like it you go do something else.

For four hours a week I'd tell them to stick it, but of she really enjoys what she does, she could try to push the shoe care in a more fun way - instead of the boring "Would you like some polish?", she could try opening her conversation with the punters by telling them how she used this really great stuff and it's made her shoes softer/shinier/longer wearing/whatever. It was only £3.99 and it's changed her life! Then show the punter the shoes with a wee line like "That stuff I was telling you about would be really good on these".

It might or might not work, but at least she can have a laugh trying.