Welcome to Apple Support Communities. As I am understanding it, you want to get the picture above back as your sister's wallpaper but you aren't seeing that as an option under the default wallpapers in settings.
If that's the case, she may have gotten it off of a previous phone of hers which is most likely saved somewhere in her photo's. You can use any photo from your photo's app as your wallpaper. Or, again you can select from a handful of option that the iPhone offers as a default.
To learn more, see here: Change your iPhone wallpaper
Don't hesitate to reach out if you have any further questions, otherwise, I hope you enjoy the rest of your week.
Cheers!
If that's the case, she may have gotten it off of a previous phone of hers which is most likely saved somewhere in her photo's. You can use any photo from your photo's app as your wallpaper. Or, again you can select from a handful of option that the iPhone offers as a default.
To learn more, see here: Change your iPhone wallpaper
Don't hesitate to reach out if you have any further questions, otherwise, I hope you enjoy the rest of your week.
Cheers!