Such great advice here; just to add that my dd24 is a joint first study (strings and woodwind) plus is a chorister; piano lessons were stopped some time ago. I would say it’s time for her to choose first study ready for auditions etc later this year - some schools will take her joint first study, but many studios will not welcome it even if its allowed. I also think she will do better focusing on one now, but of course still playing the other but that’s because she is so busy and covering so many ensembles etc that she simply doesn’t get practice time to cover two. So something to keep an eye on with your DS over the next few years, and of course piano is a much more usual joint instrument esp for jazz players. And there is no one size fits all on this journey!