Reading the Tafseer would help Sister. (I suggest Tafseer Ibn Katheer, its great)
Trust me.
And as ‘Allaamah Muhammad Ibn Ibraheem said, “It is impossible for Allaah to call someone a Kaafir for ‘Ruling by Other Than What Allaah Revealed’ and then for them not to be a Kaafir.”
Here is what Ibn Katheer said in this Tafseer (Volume 2, p. 63-67)
“And as for the royal policies, which the Tartars were ruled by, they were takn from their king, Genghis Khan, who laid down for them al-Yaasiq, which is a book made up of laws which he took from different shari`as. It is from Judaism, Christianity, the Islamic religion and others. Also it contains many laws which he took from his sheer thinking and desire. Thus, it became within his sons a followed law to which they have been gibing precedence over ruling by the Book of Allah and the Sunna of His Messenger. Whoever does this is a kaafir that must be fought until he returns to the rule of Allah and His Messenger.”