Although this is a question of personal interpretation that relies heavily on the reader's perspective on love, there is quite a bit of evidence in the poem to indicate that Bess's actions are brave and purposeful rather than foolish.

The reader discovers in the first part of the poem that Bess and the highwayman seem to truly love each other; their relationship is not one-sided on Bess's part. In the last stanza of part 1, after the highwayman promises his "bonny sweetheart" that he will return to her, it reads,

He rose upright in the stirrups. He scarce could reach her hand,
But she loosened her hair in the casement. His face burnt like a brand
As the black cascade of perfume came tumbling over his breast;
And he kissed its waves in the moonlight

Part 2 is the section in which Bess is tied up by British soldiers as they await the highwayman. However, they do more than simply tie her up. The poem claims that they snicker, joke, threaten, and kiss her. Their actions speak to possibilities of what they might continue to do after the highwayman's death; there is no reason to assume that they will release her once he is caught and killed. So, faced with the likelihood of further taunting and molestation along with the knowledge that the soldiers are there to kill her lover, Bess first contrives to get free.

Dying is not her first plan. However, when the bonds hold tight, she changes tactics and gets hold of the trigger of the gun that is placed under her breast. With seemingly no other alternatives to get free and warn the highwayman, Bess pulls the trigger. With her death, she deprives the soldiers of anything that they might do to her and, more importantly to her, alerts her lover to the danger waiting for him.