[Milu]

My first reaction was to say: Just give her her marching orders. But she is your sister and it seems she has some issues beyond not paying her dues, I think you have a responsability to get to the bottom of that.

Start by gently and politely telling her you are pissed about the situation and that it ends now.

Establish that with her new job she can pay all her commitments and try and find what the root problem is - it could be anything from being a bad money manager to being just personally disorganised to having a lot of debts you know nothing about.

From that you have to decide how to go forward together. It's likely she needs no more than a lot of initial help in organising her finances and a wakeup call about her responsabilities to the household. It might be better if she finds her own place.