This is an excellent question. As you go through the play, it is clear that by the end of the play the major shift of power that has occurred has been the transfer from the matriarchal Mama to her son, Walter. Note how at the beginning of the play Walter tries to do everything he can to persuade Mama to give him the money from his father's insurance cheque to invest in a liquor business. However, at the end of Act One, it is clear who is the real head of the family according to Walter:
What you want me to say you done right for? You the head of the family. You run our lives like you want to. It was your money and you did what you wanted with it. So what you need for me to say it was all right for?
However, perhaps because of this speech and the way that Walter feels Mama has "butchered his dreams," in Act Two Mama has a change of heart, placing him in charge of the rest of the money and giving him the headship of the family:
And from now on any penny that come out of it or that go in it is for you to look after. For you to decide... It ain't much, but it's all I got in the world and I'm putting it in your hands. I'm telling you to be the heard of this family from now on like you supposed to be.
Of course, as the rest of the play goes on to show, this was perhaps not the wisest of decisions, as Walter is quick to lose the money. However, ironically, this gives him the chance to assert his authority at the end when he refuses the cash-offer from Lindner to not move into their new house.