Dealing with huissier du justice

This is messy. 

I have two sons who live with me. One has autism and I cant praise French Social Services enough for their support.

Their French mother, whom I separated from in 2002 is forbidden to enter the same town as the children. It was a female judge by the way.  Enough said on that.

In January of 2017, her daughter turns up at my door. I've known her since she was 8 years old. Her own parents had turned her out (separate addresses). She is schizophrenic, delusional and prone to suicide.  She stayed until January 2018 with two stays in psychiatric hospitals. She was making progress with her treatment until she met a young man and moved out.  Last I heard she was back in hospital.

The huissier du justice are now after 45 Euros she owes for some insurance. It's a piddling sum and I could easily pay it for her except, it would set a precedent.  (Been there before with her mum).  I wrote to the huissier du justice explaining she no longer lives here. I also phoned and explained she has been absent for over a year and I don't expect her to return.

They are not letting go.  I'm no stranger to legal disputes and in no way intimidated easily yet, I'm not sure how to deal with these people if they turn up at my door.

Any advice?