Unfortunately, Kindle Previewer is not very reliable, when it comes to the preview of RTL text. It also seems to use installed system fonts, because when I openend your file, all three lines were displayed in the same font, because neither Nazli nor Lateef are installed on my system.
On my K3, the actual display was even worse: all of the Arabic characters with vowel signs on them were displayed disjointed.
AFAIK, the only thing that you can do is install a font hack. IIRC, an Arab Kindle user managed to install the Arabic Droid Naskh fonts on a PW using the
USE_ALT_FONTS font hack, but that hack seems to work only with certain firmware versions without a jailbreak.
@curious non-Arabic speaking Kindle users:
The Arabic phrase shown in the screenshots is the first verse of a Qur'an Sura (
9:111).
(Unlike most other Arabic texts, the Qur'an is traditionally written with vowel signs.)