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Hello and welcome,
There is nothing you can do to persuade your sister to change her ways if she is not willing to do so. If she were to acknowledged that she has a problem then she would also have to accept responsibility for it and she's not prepared to do this.
As you have said yourself, she is irresponsible and this is the main problem, along with dishonesty.
It is very difficult when someone we love acts in such a way as to totally go against our values and everything we believe is right. As well as doing this, your sister has also put you in a position where you have been forced, by your conduct, to personally deal with the effects of her behaviour (demanding money when she has no intentions to repay and compromising your position at work). I mention this because she could be irresponsible but do so in a way which didn't affect you so much, but she chooses not to. This indicates that she does have some difficulties with close relationships in her life. Is this evident in her other personal relationships?
Clear boundaries are needed in your dealings with her as she is currently putting herself in a position where you either have to reject her or continue to facilitate her irresponsibility. Her actions need to have consequences on the relationship if she is to be encouraged to accept responsibility for her actions. She is likely to perceive this as rejection. It isn't, but by viewing it this way she can blame you rather than take responsibility for the situation.
You will always love her and there is no reason why you should not continue to express this, along with interest in her welfare. But if her irresponsibility means she takes from you without regard for your welfare, then the appropriate response is to take a step back. If she is caring, she gets to share more of you. I recommend you consider setting clearer boundaries with her in this or some other way.
If it helps you can see it as preserving your love for your sister until such a time as she can benefit from it, rather than allowing yourself to become alienated from her through her conduct such that you never want to see her again.
I'll pause here to see what you think of my comments and to check if you have any further questions.