Girl applying herself to vinaigrette? (5,8)

I believe the answer is:

salad dressing

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'vinaigrette?' is the definition.
(vinaigrette is a kind of salad dressing)

I can't explain the remainder of the clue.

(Other definitions for salad dressing that I've seen before include "saucy thing!" , "leaves having taken this coat?" , "Vinaigrette or mayonnaise, for example" , "Eg, Thousand Island or French" , "Mayonnaise, e.g." .)

I've seen this clue in The Guardian.

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