Why does my Sister need an alternate email account to register in yescrowd?
She cannot access web services at the moemnt to set a new email, as her existing receives 100 + rubbish every day
It takes 10 minutes to set up a free gmail account.
It sounds like your sisters current account is a bust anyway with that much spam. She shouldn't be using an ISP email account IMO as that tends to lock you into staying with Optus. A free GMAil account has better security, spam filtering, recovery and other features and is ISP agnostic.
Your sister's Yes Crowd should be linked to her MyAccount meaning she should be able to log in with the same e-mail address she uses to access MyAccount.
Web services was undergoing planned system maintenance over the weekend, hopefully she should be able to do what she needs to do now?