The sentence was Mari is listening to the violin playing of her brother Sunny.
- Translation I landed on, as dramatic-anime-yelled by Basil above:
Mari je sluša violina igranje njezina brata Sunnya.
- Translation from Weeb, an actual native speaker:
Mari sluša igranje violine njezinog brata Sunnyja.
Google Translate parses my attempt well enough, though obviously I still missed a few pieces. It did legitimately take an hour!!