The protest
Marie Ursule is presented as a loving mother and devoted person. As such, we may see her actions of protest in ironic contrast to this.
Flowers and poison
Marie Ursule ironically gathers poisons in the way others "might gather flowers." This is ironic because poison obviously has much more violent connotations than flowers.
Picking plants
Marie Ursule's picking of plants is ironically compared to a "fervent lover." This is ironic because she isn't actually picking the plants in a loving way.
Faithfully
Marie Ursule is described as collecting the plants "faithfully," which is ironic because 'faithful' isn't the word we might expect to describe her devotion to her protest.
