idk how to explain it concisely, but it feels like a really poignant allegory for past abuse and the poison it leaves behind in future relationships. her aunt may have been trying to protect her, but what she did in reality left bella isolated and hurting for a very long time. so the curse is literal but also symbolic of how the scars of her past continue to poison people she cares about. and it's interesting because, her aunt set the conditions, right? she said "if you're hurt, the right person will eventually come and save you," and the setup implies that from basically the beginning.
but it isn't anna's love itself that saves her but her choosing to love anna. love is a really vulnerable thing. it's terrifying to be exposed like that, and poison is a plant's defense mechanism (much like trauma-based issues were at one point helpful during the trauma, but now only make things worse). the actual healing only occurred when she let that wall down and opened her heart, and it required her to actively decide and retake what was important to her. if you think about it that way, it's kind of like the RGU finale? similar thing going on, but imo this is twice as romantic. beautiful story and art