Octavius consented to this.

He, in fact, assisted Octavia in making her preparations.

It is said, however, that he was influenced in this plan by his confident belief that this noble attempt of his sister to reclaim her husband would fail, and that, by the failure of it, Antony would be put in the wrong, in the estimation of the Roman people, more absolutely and hopelessly than ever, and that the way would thus be prepared for his complete and final destruction.
Octavia was rejoiced to obtain her brother's aid to her undertaking, whatever the motive might be which induced him to afford it.

She accordingly levied a considerable body of troops, raised a large sum of money, provided clothes, and tents, and military stores for the army; and when all was ready, she left Italy and put to sea, having previously dispatched a messenger to her husband to inform him that she was coming.
Cleopatra began now to be afraid that she was to lose Antony again, and she at once began to resort to the usual artifices employed in such cases, in order to retain her power over him.

She said nothing, but assumed the appearance of one pining under the influence of some secret suffering or sorrow.