Why does Rachael stop Stephen's wife from killing herself when Stephen seems to be powerless to act?

Stephen has fallen asleep in his wife's room. He has troubled dreams which reflect his troubled life. His wife is a drunk and his home, which is supposed to be a refuge, has become an extension of his bleak reality. Stephen is half asleep when he sees his wife reach to take her whole bottle of medication in an apparent suicide attempt. Rachel steps in to stop her, crushing the bottle in the process. It is unclear if Stephen was too groggy with sleep to stop his wife or if he simply might have wanted her to kill herself. Did he, perhaps, think it a dream or even fantasy? The event only serves to reinforce Stephen's feeling that Rachael is an "angel".

Rachael's action where Stephen does not make a move to stop his wife from taking the bottle contrasts her kindness and optimism with his pessimism. Whereas he has been beaten down by the injustices of the novel so far, so much so that he's confused whether he could cause harm to his wife or not, Rachael works to keep his spirits up. She wants him to commit to living. As such, it makes sense she would preserve life where Stephen, so uncertain about what actions he should take, does not take action.