Tell her she owes you money and you demand full payment right now. If she refuses tell her to leave and never come back. If she comes back, have the police trespass her from the property. If she returns, call the police and have her arrested.
Don't let these kinds of idiots create stress in your life. It's simple really. Nothing wrong with firing a "customer".
Acting nice to her is not doing you any favors. Take the kid gloves off and handle the problem.
That's the answer right there. Cut her loose and be done or you will just be on the hook working for free evermore. I have dealt with people like this forever and believe me this is the best answer for you. This type will just keep coming back and take whatever they can get and they lost any sense of shame they had long ago. They know two things only,what they need and where to try to get it. Of course they have no real sense of need vs. want and will always buy senseless [censored] then go begging for what they need to live. They always have "PROBLEMS" and you will feel sorry for them possibly for a bit until you get to know them better . Then you see the pattern of self destructive behavior and recurring problems over and over again. If you start doing favors for them you can be sure of one thing, they will be back for more until they burn that bridge and then they move on to someone else who feels sorry for them.
I dealt with a HUD woman for around 10 years in a rental situation. Same sort of thing. Always short of cash for the pittance that she owed herself. At the same time she managed a bigger screen computer then a big screen tv than I had while I was making good money. Cell phones, Satellite tv, cable (grab the deal then disconnect for non payment) and all the rest. She always managed to nickle and dime me so I missed a couple hundred / year and so it went. You get the picture. It never changes. When I finally got rid of her I took 7 pickup loads of busted toy, old magazines and general trash away.
In the end your best bet I have found is treat them like a bad kid because that is what they are. If you are overly nice to them then their problems slowly become your problems until you end it. Don't wast your time and expense trying collections on this one as you simply can't get blood from a stone and you will never see a dime and just have to pay the county to file the paperwork. Next time she comes in begging show her a copy of the bill she didn't pay and tell her you can't do anything more until she settles up, PERIOD. If she hangs around and babbles(and she will) at you as this type often do make an excuse you are busy and go do something to get away. If she starts getting uppity get the boss, [censored] he ought to be handling this stuff anyways.
There is no solution for people like this
and eventually she will end up a bag lady pushing a shopping cart around if she lives that long and its not you problem. In California just like NY these folks have plenty of help if they go look for it but either way it's not your problem unless you make it your problem. Let her go beg from someone else and never look back.