Tenant and contract question

[Robin Brown]

So my partner has a tenant in her flat, she also self manages the apartment herself. Recently the tenant wanted to negotiate a new deal and go month to month with a reductions due to COVID stuff down here in Melb.

The contract was these two options.

Stay on a 6 month lease for $320 pw

or

Month to month at $340 pw

Tenant has taken month to month - It has been 4 months. The tenant has now decided she would like to stay until Jan or longer. And wishes to pay $320 in rent instead of $340 and would like to be reimbursed the 'extra' she paid the previous four months.

Obviously I feel that's a bit foolish as just because you have changed your mind you signed at that price, a new lease will now need to be signed and negotiated but no reimbursement.  How would you handle this situation?