Hi Nuckle,
Maybe you should just book your friends helper for those dates... I bet she'll let you know if she wants more than you usually pay her. But if you're in holiday spirit and all, you could offer her a bit more than usual to make her more satisfied and feeling appreciated... also, you can enjoy your time with good conscience. 70-80 HKD/hour is really not bad... I'd offer something like that... but this is just my opinion...
DS :cheerlead