If you apply the payments to the late fees first, then the rent, then they just wind up owing you rent which you can put on your notice. I'm not sure how it is in Florida, but in Wisconsin, there are two forms. One is a "5 Day Notice to Pay Rent or Vacate" on which you can ONLY put rent amounts. The second is a "5 Day Notice to Correct Breach or Vacate".
So if the tenant owes rent of $600 and a late fee of $50, you'd actually have to send out two forms, one form for the rent and the other form for the late fee.
Maybe you can check to see if Florida has a similar set of forms?
I only accept the rent if it is paid in full, no partial payments. If the tenant is late then they must pay the late fee and the rent payment or I don't accept it. After 3 days I serve them.
As for the money that you are owed, I normally take it out of their security deposit.
We apply payments to the oldest outstanding charge first. Then whatever else is outstanding, such as rent, we are able to file evictions on. As far as the utilities go, we warn the tenants that we disconnect utilities within 3 days of them moving in. We also have a form (here's a link: http://alhpodland.com/alhpodland-rental-homes-tran...) which they have to fill out PRIOR to moving in. I'd send them a notification that utilities will be disconnected immediately (and shut them off) and add the charge for the utilities to their account.
Hope that helps.
In my experience this tenant will never catch up. I would give her a date to pay the late fees by (no more than a week from today) and if she doesn't pay them then just start the eviction. At that point if she has something to lose she will pay you.
Send out the notice of termination of tenancy. This is only the beginning. I'd rather have her out then get the late fees.