she needs to separate your relationship with her brother and the friendship she has with you, and also the actions of your family are not yours either. if she is not willing to do that or see that then she sadly maybe she doesnt value your friendship past a “sister in law” status.
may i ask what does your entire family have to do with the friendship between you and her? was the altercation to with the break-up or her.

Perhaps you can have a sit down with her or text her to express how much you value your friendship with her. that you are sad and affected about the end of the relationship and although you do love her brother it just couldnt be? and can she separate your friendship from your relationship?

if you have come to the point where you dont want to try to work on the relationship with her further, first recognise what you could have done better and know within yourself that you will work on you. and forgive yourself. like this you will have the inner strength to move on, head held high 🙂

Good Luck