A smart girl would do the following:

1. Register a business name with a brand like Sarah's Office Sandwiches. You don't need to be a permanent resident to register a business name. Must use real name.
2. Open a bank account in the business name. Tell the bank she makes and sells sandwiches door-to-door (office to office) and her business location is her home (no need to have commercial premises)
3. this way, when the bank sees lots of cash deposits, it will look legit.
4. Declare only around 25% of the bank deposits as her net income before tax. The remainder would be considered business expenses (cost of sandwich ingredients and travel, etc.)

As other punters have written, every bank is super-sensitive about seeing cash deposits today. They "debank" hundreds of clients every month. This word debank is now common.