Ok, I can see a teaspoon of seeded mustard in clam chowder....but not the vinegar. Wouldn't the vinegar curdle the cream?
I'm sorry - I have no practical advice for you - and you also have the distinction of being the first person I've seen who's written this problem. However, I can say that I never did resolve the problem of my ex-husband putting too many random herbs in his spaghetti bolognaise. Though divorce did eventually solve the issue once and for all.
While it's lovely to have someone cook for us, the enjoyment is based on having food which is edible. Perhaps she could compromise? Perhaps cook by a recipe 75% of the time?
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.