I think it's very pretty, well known but not popular, but perhaps feels slightly dated (my first references would be Rosanna Arquette and the 80's Toto song named after her and it isn't as classical feeling as the similar Rosalind/ Rosamund).
However it has such a nice sound - "Rose - annah" as opposed to the harsher "Roz" sound of other names so I can see why you'd choose it and it has nice nickname options too if she wants.