Hi Rosedance

Welcome. It sounds like there has been a lot of chaos in the past, when she was living in the family home, and long after she left because of a "vicious campaign of hate, anger and revenge." It sounds like it must be highly stressful.
Do you and others in the household feel safe (including emotionally) to invite her back?
It sounds like it has been stressful enough without her there (thinking of her vicioius campaign of hate, anger and revenge). What would it be like to have her back inside the home?
If she's saying she is almost homeless, she may have had some bad luck, or she may have made poor choices along the way. Either way, it sounds like she feels entitled to return home, without first asking. That doesn't really sound like someone who is ready to contribute in a healthy way to making deposits as well as withdrawals to/from the family unit. Inotherwords, are there more benefits than disadvantages? Will she pay rent? Will she help with the cleaning? Cooking? Laundry? Will she bring health and humour to the family dynamic, or will she bring chaos? Will she bring a sense of safety? These are important things to consider. There are probably many other things to consider that we don't know about.
The family doesn't "owe" her. She is an adult now, and responsible for herself. The family is not responsible for her. It is the family's
choice to support her by inviting her back home, offering support in other ways (just keeping an open line of communication), or keeping a safe distance. Inotherwords, there is no obligation to take her in because you are family. Her past behavior and lack of respect to the family is a consideration.
An option, would be to offer suggestions, such as a women's shelter, looking at rentals, etc.
But then again, perhaps you don't want to do that. Perhaps having her in your town/city might be too close. It depends on the situation, and how safe everyone feels. Right now is the time to make your boundaries clear. That's the easy part. If she came to live near you or with you, enforcing boundaries once she is there, would be the hard part.
Do you know what her history has been since she left home? Has she had brushes with the law? Does she have any debts? Has she, or is she using drugs or alcohol? You have a right to know what she has been involved in since she left home.
Consensus and agreement between you, your mom and your sibling is important, whatever the decision. There is no easy answer. Any decision will probably be hard.