I'd certainly consider a wetsuit for her, help keep her
core warm. I'm a
member of a sailing club here in Tasmania (the island just south of the SE corner of Australia), and our children's sailing program recommends a full light suit, not a shorty. The water's pretty cold here, and they practice capsizing the dinghies and then sailing them, so the kids are in the
water A LOT. Don't know what your program is, but assume wet & cold till it gets warm.
Ann