I guess it depends on how long ago .. and whether they are/were cloistered. For those who have truly and fully "given up the world", there is no other name for them except the one they take upon final vows. So Phoebe Figalilly becomes Sister Mary Epiphania Therese (no last name).
I don't keep up with the modern traditions regards Sisterhoods, so I'm quite happy to accept it is different from the way it was .. plus different Orders do have different traditions and different places also.
I don't think most priests take new names, these days, do they? (Most of them probably have a good Saint name taken for confirmation (if they even do THAT now).)