Property sold by mother

If she wants to get exemption benefit over LTCG on sell of the house, she can purchase new house as joint holder along with yourself.

Is the indexation benefit still available and how can we calculate same . Want to see if she is liable for tax at all

Yes, indexation benefit allowed, Tax luability will be nil if at least the net LTCG is invested in new HP.

Just trying to understand what is the benefit of buying in joint ownership vs only hers. 
Her intention is I should buy directly in my name to avoid any change of ownership later or having will.

Need more suggestion as someone also suggested that mother can still claim LTCG even if she buys property for son..please suggest.

Also another reason is she wants to avoid any will, transfer issues later for me so what would be the best possible way.