I would charge late fees, and apply payments received to late fees first and then lot rent.
So if she owes $300 + a $40 late fee in February, and only pays $300, she still owes $40 in unpaid rent in March, and I would invoice her for $300 March rent plus $40 unpaid February rent. If she pays $300 late again, i would apply it to late fees, and now she owed $80 in unpaid rent. Tighten up the wording of your lease if you need to in order to implement this.
I’m not an attorney, and I would ask your attorney about this. Is the judge preventing you from evicting for nonpayment of late fees (common) or is the judge saying you legally can’t charge late fees ever? (uncommon)