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Sadgirl101 If they are really true family and friends, they should know both of you better and scold her for it.
If they see it as bad and they let it pass, then that is called enabling.
You can do the hard choice and save yourself. Be there for your niece on occasions. But for now, it might be better if you step away for a bit.
Reality is you have your life and it's your choice whether to stay or go. You cannot change people, but you can choose which people surrounds you. You can choose to change your environment and yourself.
Make the choice and follow through. Whatever you choose, you should know that no one deserves to be a doormat. You teach people how to treat you by what you tolerate. You might as well set boundaries and limit their access to you. It would be good for your mental health in the long term.
But again, only you would know what would help you breathe easier. Do what is best for you.