The Hilda series are often surrounded by adventure, mythical creatures and monsters, and other aspects that make it quite exciting and adventurous, so Hilda learning to play an musical instrument might not fit that elevated criteria, however it could perhaps be a subplot, perhaps Hilda could ask Wood man to teach her, and after that it could be something that she would be seen doing from time to time, but not as an entire episode, and after continuous lessons, (at first she could struggle to learn it, being harder than she previously tough, and almost giving up, but eventually learning under the guide of Wood man), she would eventually master it.