Except Manga Lillie really didn't do a whole lot besides have a PTSD episode... that kind of went nowhere. While her confronting Lusamine was nice... it isn't like any other version of this story. Not like SM where Lillie had that stand up, not like USUM where we got implications and the aftermath to see... and not like the anime where the circumstances are different, but her call out reached to her.
She never blew the flute, never really showed much growth in between, was NOT there for most of the mother beast stuff and it looked like she forgotten about Nebby.
How is this any better than what the anime (Different story despite keeping the events.) and USUM (Different route and reduced focus, yet still the same character arc.) did?
Lillie's overall role in the manga is one of my biggest complaints, mostly because most that made her arc stood out... isn't really there. (I do however REALLY like what happened and how Lusamine snapped out of her crazy. Honestly, Manga Lusamine is what SM Lusamine should have been from the start.)
On the bright note, it disproved an old theory that was speculated by the SM games and was seen as a plot hole in USUM. (Lillie's dress. Despite similarities to a certain UB, it was ultimately just a coincidence and it was really Lusamine's mad attempt at keeping her kids from changing.)
So anyone saying her switching to her Z Powered Form in USUM had less meaning because Lusamine wasn't obsessed with the UB's are now proven to be full of it and they can shut it! It's still a metaphor to Lillie having the newly grown bravery to take life as her own and make her own choices. Which fits well with how USUM wrapped her story up, with the goal of becoming stronger so she can better protect those she cares about.
(Wished she still had the same amount of narrative focus as in SM. That is my biggest criticism with how USUM handled her. The route was fine, but the reduced focus... weakened things.)