The manufacturer should pay you a retainer as ambassadress.
From the guardian.co.uk
The advert, which is almost two minutes long, was directed by fashion photographer Mario Testino and is Watson's first role as ambassadress for the brand.
From the telegraph.co.uk
America loved Grandma Moses as the representative of natural virtue-the ambassadress of a past that was al ready being sentimentalized on an industrial scale.
From the time.com
More examples
A woman ambassador
[new] (1) The wife of an *ambassador (sense 1). The title in this sense, which was merely a courtesy since the wife possessed no *representative character in her own right, came in following the introduction of the *resident embassy in the mid-fifteenth century. ...