I think it might be a health issue related to gravity. Earth's gravity is different from the room she was in on the spaceship. Every astronaut who goes to space experiences health problems, you can research it. The longer the stay, the worse it gets. For those who can't understand that the gravity in the spaceship's room was weaker, just reread the part where her father can't maintain his humanoid form outside of Earth's environment without Miria's help, but he could in the room in the spaceship. Our gravity is essential for our survival and well-being. I can't imagine the damage it would cause a baby growing up in space... fragile lungs and bones, all the issues with fluid balance, a total mess!
oh nooo lilyyyy wdym she's slowly dying