A few scenes after the failed suicide attempt of Shouko, we see Yuzuru telling her mother something about the pictures she was taking and how she was trying to prevent Shouko from killing herself. Can someone explain that to me?
From to the wiki,
Her hobby is taking pictures of dead animals, with the intent of showing her sister how horrible death is. The purpose is to discourage her sister from killing herself.
Yuzuru's hobby of photographing dead animals was born from her desire to discourage her sister from committing suicide. This is confirmed in the A Silent Voice manga. In volume 6, Chapter 45: It Was All For Nothing, there is a flashback where Shoko tells Yuzuru she wants to die. On the same page, Yuzuru tries to figure out what to do, stating
What can I do? How can I make her not want to die?
Before the flashback ends, her focus shifts to some sort of carcass and she thinks, "That's it!"
Furthermore, earlier in the chapter before the flashback, Yuzuru is seen taking down the photos, and when asked why by her mother, she replies,
Because I realized they were meaningless. I thought seeing these would change her mind about wanting to die.
In volume 4, at the end of Chapter 32: Gum Syrup, we see a glimpse of Yuzuru's motivation for taking the pictures. When the others show Yuzuru a bird's corpse, she takes a picture and then immediately asks Shoko if she thinks the corpse is gross. Shoko makes a disgusted face and sticks out her tongue, prompting Yuzuru to excitedly clamor,
Oh?! You think it's gross, huh?!
A little later, when it becomes apparent everyone is trying to cheer Yuzuru up after her grandmother's death, Yuzuru states,
In that case, you guys don't understand me at all!! Did you really think this would make me happy?!
A bit of a stretch, but this might possibly hint at the pictures being for her sister, not for Yuzuru herself.
Though there are some unanswered questions, such as whether Yuzuru genuinely enjoys her hobby or if she just does it for her sister's sake, the manga makes it clear that Yuzuru is trying to gross out and disturb Shoko with the pictures so that she doesn't kill herself.