@jim.cox I work for ANZ so will shed some light on this.
1) It is important for you both to have separate IB accounts - this is possible as with a joint account you both have customer numbers. In this case, you were operating the account through one customer number which is also a breach of the internet banking terms regarding protecting your password from third parties.
2) If it was a 2 to sign account the IB platform will refuse to allow a transfer through the interface. Furthermore, it is possible for staff to lock down accounts to "view only" mode where you can transfer money in, but not take it out.
In your case you were not using it properly and if you're still an ANZ customer I advise you to call up their contact centre to get internet banking created for your wife under her own customer number. Once you do this then you have by default a separate Online Code mobile number.
Edit: Further clarification was done via PM. In this case it was wanting to set 2x mobile numbers on a single IB login which is not possible for security reasons and what sounds like to be sharing logins.
You're 100% correct here but I do wish there was an easier option with ANZ Online Banking for mulitple phone numbers. For businesses with multiple signatories this can be a pain as the Online Banking only allows one login/password and one mobile number.
There is ANZ Direct Online but that's overkill for 99% of small/medium sized businesses although AFAIK it's the only option for two to sign accounts (tell a lie - there is a workaround for online banking but it's a PITA)
The BNZ allow different logins for business (e.g. access number/customer number, user ID, password)