Noun-noun modification: as always in English, Word Order Counts

So,Jeopardy! had a category where the answer was three rhyming words. One of the clues was "Mother in a cute movie about a guy and a girl". The contestant answered "What is a mom rom com?"

They gave it to her.

Nope.

In English the head noun - the one that is what you're talking about - is the last one. The preceding nouns modify that one. What kind of modification, precisely, is unpredictable, but "sports journalist, woman journalist, magazine journalist," and "crime jornalist" are all journalists. A "race horse" is not a "horse race" and a "dog house" is a different thing than a "house dog."

And a "mom rom com" is a movie. A "rom com mom" is a mother.