That is sad, to lose two people you love in that short a time span. I'm sorry.
Something in your wife's life must have been very unbalanced, for her to take her own life. The daughter, was very dependant on her mother in more ways than one. The emotional support was a big issue for the daughter. Her mother was her rock! With out her she was lost and felt she was living a useless life.
I'm sure you must have some idea why your wife took her own life? Correct? If you truly don't then let me know and I'll see why?