Peace be up on you
is a kind of prayer
Prayers are forbidden for non-Muslims
So, we can't say (peace be up on you) we only use with them (hi or hello)
The same is said for the nurse if she is non-Muslim how we call here (sister)?????
This is the answer for your question
and I would like to draw your attention to s.th
The word (priest) is used for Christians which means in Arabic
كاهن قسيس
put if want the same expression in Muslims life ,we use (scholar) or (shaik)
عالم او شيخ
So nice to put this topic for Islam service .