I see a lot of people say that the whole point of Lace's story is that she's not a child, and putting aside my stance on the age debate, I just feel like that's not entirely true?
Personally, I think the point of Lace's story is that she is alive, and that her life has worth.
When we talk to her in the Cradle, everything she says is all about how she's 'pathetic, crudely made, and nothing more than an empty husk.' Hornet combats this, saying she in fact IS alive, despite her unique circumstances, and Lace doesn't believe her, thinking she's only speaking in platitudes. Her needolin dialogue is about how she wants to be seen (by her mother specifically), to be acknowledged. She wants to be good enough, which also kind of ties into her life having worth. Cause if she's not good enough, she'll be discarded like Phantom was.
When we meet her in the abyss, she's fully accepted her own demise in exchange for getting revenge on her mother. When Hornet talks about wanting to save the kingdom (and by extension her), she pokes fun at her thinking it's not only not possible, but not worth it. "Join me in my drowning palace and let oblivion swallow us all". If her life has no worth, or didn't exist in the first place, what value is there in saving it? But then Hornet does save her anyway. Maybe to get Granny Silk to let go, maybe because she just happened to be there and saveable, or maybe because she fully intended to save her. But the point is that Lace is proven wrong. The kingdom was saved, and so was she. She was worth saving. If that makes sense.
There's this one line Hornet says in the Cradle that's kind of stuck in my mind: "Yours was life, pale one. Do not confuse your unique creation with its absence. I have seen others make the same mistake." And I think this quote really kind of sums up my whole interpretation here. Her was life, despite what she thinks. Now this quote is kind of on the nose, so it's quite possible that I'm missing a shitton of subtext because I've admittedly never been good with that, but I think it makes sense?
And that last bit in particular, "I have seen others make the same mistake" really makes me think about how Lace parallels Ghost and THK, especially from Hornet's pov. The Hollow Knight probably didn't think of itself as alive; its entire purpose was to be hollow and contain the radiance for all eternity. Ghost nearly had a similar fate. All three of these characters were created to serve a particular purpose, to fulfill a role rather than to live as people (or, bugs): The vessels to contain the infection and be hollow, and Lace to wish her mother's waking and be loyal. (And then it gets messier once you bring age into the equation but again, this post isn't about that) To Hornet, she's watching this same cycle she saw with the vessels all over again through Lace. In a way, her saving Lace in Sister of the Void can be thought of like a second chance. She couldn't save Hollow from being sealed, she couldn't save Ghost from sacrificing itself to kill the radiance, but she can save Lace. "This one... the dark shall not take." The vessels may not have been 'alive' in conventional sense, but they they still had life, right? Same goes for Lace. And all of their lives have worth.
And then that actually segues into a really interesting question that these stories pose of what does it mean to be alive? What counts? What are the conditions?
Anyways uh yeah I don't really have much left in me that's about all I got. I'm not good at analysis, this is just me attempting to sound smart and write a lot. I might be wrong. Feel free to correct me (NICELY)