I dont get it, doesnt google only allow one account per household? I mean how will they no know if I have five account but under different names and bankaccounts?
Acoording to google it's fine. You just can't have 2 accounts under the same name. https://www.google.com/adsense/support/bin/answer.py?answer=9729&topic=8429
it's risky! to use different account under same Ip. One or one day adsense bot will detect two different log in from same Ip and will report as fraud and your account may be banned. Use same account create a seperate channel for your sisters website. or Better contact adsense and ask about that.........
Have you readd this? Publishers are not permitted to maintain multiple AdSense accounts under the same payee name.
So - they can use separate channels. Still I think the sister should just apply for adsense if she has a website which gets decent visitors and they should tell google in the application that there is another adsense account in the same family.