Maria died with alot of regrets. She wouldn't live long enough to see her boys grow up. She put them in danger by leaving them alone with her husband. She would shatter Max in a way he would probably never heal from and give Tech so many problems without leaving him something to show she cared for him, and Rai would hate her forever.

When she sealed Rai it wasn't to get rid of a monster it was to protect her sons. She wanted nothing more than to run away that night and hide from Kuro, to at least get a chance to hold her newborn in her arms and sing to him like she did for Max, but the child would have grown up hateful and her boys would suffer alone. At lease this way they would always be together, even though they may suffer more they wouldn't be alone.

If she lived she would have loved Rai no differently from Max, but she was not there to show the love he needed, so she sealed him and made a fake personality, one that she hoped would show the love and caring nature she wished she could have shown Rai, one that no matter what wanted nothing more than to keep everyone together. She didn't think that her hope would want to live as well as Tech grew, and instead of being a protective shell became determined to protect everyone and had become the very person that poured her heart into making sure they were safe.

Exactly as Max saw it, Tech became Maria's second chance, the living personification of Hope.

(Sorry for the inconsistant writing. Hard to think when you feel all emotional. I blame this song http://www.youtube.com/watch?v=wasYNNfnfVE )