She should choose to focus on the instrument that she prefers if you only want to pay for private lessons for one instrument. My daughter plays several instruments (practices five different instruments daily including piano). Over the years she has taken private lessons for all of them, though not weekly for all over all of the years she has been playing. She would love to take on more instruments. But now that she is heading off to college she is planning to refocus on her first loves–flute for concert bands and tenor sax for jazz bands. And she is not planning to major in music–just loves it.