Usually you'd euthanize something because it's in obvious pain and/or suffering. Because she doesn't seem unhappy or sick I don't see the problem here? At the end of the day it's all down to a yours and the vets opinion, I'd recommend getting Luna checked out to see if there's anything physically wrong with her.
HTH
I use a point and shoot for all my photos. Darken the whole room except directly over the tank, make sure it's on macro (the flower icon) and try to set the ISO as high as possible if they're coming out blurred.
HTH
No worries. Thanks for the guppies, they've settled in well. You know how to attach the Windelov Java Fern, right?
Dwarf puffers look awesome, looking forward to that tank.