am pretty sure that loaning out money in this form is illegal irregardless of part time work or not.
in order to run a business lending out money, you need to be licensed by the government. not doing so carries up to a HKD 100,000 penalty and 2 years imprisonment... -> see money lending ordinance
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the question is whether your helper forms a money lender that falls under this ordinance. if she loans only to her close friends, i guess that would be ok. but the way she is running this, she must be falling foul of this ordinance and the DH ordinance at the same time