Why does Tituba get locked up in jail with & why does she go crazy?

In Act I, Tituba is accused of being a witch by Abigail.  When blame falls on Abigail, she is quick to blame Tituba for everything that happens in the forest.  Tituba is then questioned while she is about to be beaten to death and admits to practicing witchcraft.  Salem's mentality did not make sense in that the people who admitted to practicing witchcraft went to jail while those who refused to admit to it were hanged.  Therefore, this is the reason that Tituba was locked up.  It is really unclear why she goes crazy at the start of Act III.  There are three possible explanations.  One is that Miller is using comic relief at the beginning of the act because of the tenseness that comes at the end of the act; the second is that being lock up for such a long time in those conditions drove her crazy; a third explanation is that she is pretending to be crazed by the devil's touch in order to keep up her act of being a witch.