This needs to look into, my church actually has grief counselling, in order to move forward and close a chapter in good terms.
(Sometimes spouses grieve and judge themselves with no grace over the other's passing)
It does take time to heal, but God will journey with her baby steps even, and heal her heart. Otherwise it is not going to be healthy for her in the long run.
Good that you have 2 other siblings to keep her company at the moment.