I came to the concertina, later in life than I wish I had! One thing that got me when I started to play, was the weight and strain on the little fingers and thumbs (English)- so maybe consider a neckstrap too. And don't forget to get something, box or padded bag, to protect and safely carry your gift!
Concertina's are a great investment, so money spent on this gift is not lost - and could be transferred to a better or different instrument should the young lady desire it.