In my humble opinion, I just cannot see that realistically happening with the personalities involved here - Willy Wonka prolific liar, con artist, manipulator of women, and Marion (someone with a weak area / blind spot / vulnerability for a romantic dream but otherwise together, very realistic, and law abiding).
I suggest that Wonka fathomed out a way to remove the money at the daily limit without having the police called, that he used another woman to front up, using whatsoever deceitful story or incentive necessary.
Anything else would be too far high risk for him - if it were Marion making withdrawals, one false move on her behalf such as asking a bank teller to lock her in the back room and call the police, and his entire life would come crashing down instantaneously. Wonka is not stupid and he is also a coward of the highest order, he assesses risk and likelihood. I imagine he would think nothing of sending a female mule into the bank on false pretences to make the daily withdrawals, happy in the knowledge that were she to be arrested, he couldn't be identified (someone he befriended using one of his fake personas) and she would be detained / imprisoned.
Horrible as it seems, I cannot believe that Marion came back to Australia and if she did, not for long, it certainly wasn't her making the withdrawals. MOO. I believe Wonka has all the hallmarks of a sociopathic extreme narcissist who could be easily capable of murder(s) if someone stood between him and his goal. Plus it would seem he literally despises women.
In terms of how such predatory abusers usually operate, the day that Marion said she would be 'going quiet' for a while is highly likely to have been her last day on this earth. Something dramatically changed that day. Were that to have happened, I fear she would by no means have been the first woman to have been 'dispatched'.
I suspect Wonka has a complicit female or maybe unwitting female partner in crime, could be someone he used and paid like a personal assistant sending on errands, possibly his wife, maybe not.
