It's quite clear from this article and others about this case that the mum and sister had been looking for her, but did not know where she lived. She was actively disengaging from every human contact, and was not in contact with anyone at all. If people don't want contact and don't respond to efforts to find them, then they can be incredibly hard to find and keep in contact with.
I don't think it's fair to suggest that they didn't care or didn't try to find her. And as an adult, she did have the right to cease contact with her family, if that was her choice, even if it was for reasons that no one else would have thought justified.