Rossetti wrote this in 1849, the same period she volunteered at St. Mary Magdalene Penitentiary in Highgate, a home for 'fallen women'—prostitutes and unmarried mothers society had cast out. Unlike most Victorian poems about ruined women (written by men, dripping with pity), this comes from inside the experience. The speaker isn't begging forgiveness or dying picturesquely. She's angry at herself, yes, but also stripp'd bare of the polite fictions that might comfort her.
The garden-plot she hasn't kept is her virginity, her reputation, her marriageability—the only real currency Victorian women had. The metaphor runs through the whole poem: she slept at noon (was careless in broad daylight), plucked her own flowers (made her own choice, wasn't forced), and now faces comfortless cold exile. The repetition of fool in stanza one isn't self-pity—it's brutal self-assessment. She knew the rules and broke them anyway.
What's startling is the finality. Most Victorian redemption narratives offered fallen women a path back through repentance, suffering, and death. This speaker rejects that script entirely. When others offer sun-warm'd sweet to-morrow, she shuts them down: Talk what you please. She sits alone with sorrow, not shame—there's a distinction. She's not asking for forgiveness because she knows the social death is permanent. Victorian England didn't forgive women who 'fell,' even once.