You can buy them from the salon on board but not the shops. However, i doubt they are much cheaper than here. In the caribbean they will sell them but they will usually be in American voltage. If you dont mind using an adapter at home then they may be a lot cheaper but give her the cheapest price you can get them at here before she goes. The other option is to ask Harding Brothers in the UK as they run the shops and salon.
2 years ago onboard Oceana my friends GHD's broke. To her, it was as if someone had died! As they don't sell them in the shops she purchased a pair from the Harding brothers salon and they were mega expensive. You'ld be better off buying them here!
Thank you didnt think about what would i do if they broke,so may be best leaving well alone.