Not knowing the whole story, it is hard to speculate but my gut feeling on the article is that if the daughter probably had strong feelings of abandonment driven by a wounded inner child caused by her mother's rejection. I think this was her motivation. The money simply represented her being finally recognised that she existed. I know how all this feels so I can relate. Thankfully, I'm well read on inner child survival and on abandonment issues too. Greed may have played a part but the fact that daughter had been on benefits for years suggest her self esteem never got off the ground because it had been mercilessly stamped on and crushed by an unforgiving mother.
I personally wouldn't chase after my mothers estate, I don't need her forgiveness or her money.
What I would say though is, and this is just my opinion, if you leave a will cutting someone off out of spite and vindictiveness, you leave a legacy of hate and as you go, you take it with you as well as leave it behind. That's a sad reflection on you, not the person you resent or dislike.
If any family were to chase after your legacy, they are unlikely to win. If they do, it's probably contaminated and not worth having. A bad omen perhaps.
But if you leave your estate to a deserving cause out out genuine goodwill and a wish to help, then even if your family are not included, at least you've left a legacy of goodness which will probably help others greatly.
I think the mother and daughter's story is tragic but not uncommon sadly but I would conclude that the daughter has suffered the most because of a cold hearted, unforgiving mother who's last act was to punish her even further. I hope the daughter can go on to find some self forgiveness and recovery because having such a mother, and without strong reserves of inner strength, will destroy every last drop of self respect you have.