Well from a war strategy POV, letting Jaime go was not the best decision.
But
I don't blame her one bit.
Catelyn has just found out that her two youngest sons are dead and she sees this chance to MAYBE save at least one of her daughters, so she takes it. She can't just sit by and do nothing while Sansa (and possibly Arya) are prisoners of the Lannisters anymore. She has to take action to save her remaining children.
But
I don't blame her one bit.
Catelyn has just found out that her two youngest sons are dead and she sees this chance to MAYBE save at least one of her daughters, so she takes it. She can't just sit by and do nothing while Sansa (and possibly Arya) are prisoners of the Lannisters anymore. She has to take action to save her remaining children.