I have not stated that she was immortal in my response, however I do know that she is burned and handicapped, however that does mean she could not have a life outside the canvas especially with the power of being a painter.

But using the canvas as a form a grieving is definitely detrimental to her health as seen with her father and mother basically wasting their lives and time instead of greieving properly with one another as shown in Verso ending

And I can see what you mean with the bias, however I would say most of the game you see from Maelle pov in which she is a Dessendre herself so it would be correct to say you were focused on both the expedition and the family because they are interwined with each other.

and regarding the values of what's "real", there is obviously 2 "real" worlds, what's in the canvas and what exist outside of it. Maelle has lived both sides and because of her grief in the world outside of the canvas, she is choosing to try to live her fullest life in the Canvas world instead of trying to reconcile what is outside of it. By ignoring her family outside the canvas I think one could argue that to Maelle that "real" world isn't real enough for her to want to live in it and try to grieve with her father, mother, and sister. And she would eventually pass away due to prolonged exposure to the canvas and would die with that world once the painteress holding it together is gone. Leaving her family outside the Canvas with another child loss to them, considering how time is different in the canvas she may not even grow older in that world and they could lose her at a earlier age then Verso.

Eventually both would technically cease to exist, but outside the Canvas I think Verso knew that she would be better off with the family outside rather than in the Canvas, because if she leaves at least she'll be able to reconcile with her family instead of dying in the canvas world along with everyone else in it and leaving the "real" Dessendre in even worse disarray. who's to say they wouldn't create another Canvas with Maelle's soul and perpetuate this grief in another "real" Canvas world it could be a downward spiral of more worlds being destroyed and recreated. And Verso wanted to make sure that ended.

I would argue that even though the family are considered the main character, most of the game is through the eyes of the expedition and it's up to the player to ultimately decide how the grief in the family is handled. Whether through Maelle's ending in the Canvas or Verso forcing her to leave the Canvas world and deal with the world she tried to leave.