Dutch savoury spices and herbs
I can't say that I'm an expert in Dutch food, but I did live there for a few years (decades ago).

It's entirely possible that the soup really was just salt, pepper and nutmeg in the meatballs.  The Dutch for 'soup with meatballs' is 'soep met balletjes', which will help you avoid having to sort through all of the 'Pennsylvania Dutch' recipes out there.

If you recall there being some green flecks in the soup, it's possible that it was finished with parsley or chives, but there's a good chance that most of the flavor was developed in making the stock -- cook down the chicken bones with onions and carrots at the very least.

You might always want to talk to whomever helped your grandmother move when they realized she had dementia -- they might remember some of the spices that she had ... and if she relied on any of the various dutch spice blends.  (many of which have an Indonesian influence)