Worried about foster sister- money and housing

[CocoNoopie]

Hi,
My foster sister is 20 years old and moved out of my parents house. Social services gave her an allowance to buy things for her new place and she is living on universal credit.
Its very hard to speak to her, but I know that she spends all her money in one go and then calls to say she has no money.
I am not in a position to help her out all the time.

My parents are living on their pension and are in their 70's. How can I help her? Social workers are always changing and she has a new one constantly. She is not working, not studying.
Her allowance goes on her nails and other beauty treatments. She buys all her groceries in Londis or Waitrose- thus her money doesnt go far.
I try to give her advice, have taken her shopping, told her to get more student budget meals etc but every month she will call to say her money has run out.

She feels that its the family's duty to support and help her. I am at my wit's end and the responsibility seems to be coming to me as my parents have grown frail...I have my own financial concerns, job, young kids....Im worried she will be told to move out of London as social housing is so scarce.
Any help/advice greatly appreciated.

Could she have a set of jars on her worktop labelled food, electricity, phone fun etc and the day she gets paid she divides the money into each. And maybe she could go to Lidl on that day and buy food that has a longer shelf life so won't starve at the end of the month. Could she even keep those jars at your house until she learns how it works? It's a terribly difficult stage of her life but children who are brought up in more regular circumstances... my ds!!...can also struggle with this so its often due to personality too and experience only can teach them. Could she give you 50 on pay day that you can then give back when hard times hit at the end?

Thank you everyone for allyour advice and kind words.
She was on the waiting list for Camhs, when she finally got her appointment, she refused to go. Social workers, support workers, GP's have all tried. The support is there but she is very difficult.

I am going to back away and put my foot down. My own mental health has taken a battering from her and my mum has been physically abused by her.