Since Nefretiri opened her eyes in the 20th century, she should not have been able to speak English at all, given that it's a lot more recent than the Egyptian she should have known. What's more, even if Duncan knew modern Egyptian, he would not have been able to speak to her since Ancient Egyptian is a dead language whose pronunciation has been lost to time.
It would have been extremely unlikely for Nefertiti to be successfully embalmed and mummified, as the process took several weeks in Ancient Egypt for someone of her stature, whereas multiple times on the show, Immortals would revive from even the most grievous of fatal injuries within minutes or hours after they die.
As the quickening begins, for a brief moment, you can tell it's just Nia laying there, intact, since it's very apparent her head is still attached.