A.G.
it sounds like she is upset because you recently changed your routine. this is an age where structure helps them build trust in the world and now she she is lacking that. we have used the nurse after naps from the beginning so i can't really speak from personal experience, but i would not let her cry it out. this only breaks her trust even more. we use a technique from the book 'the baby whisperer' called pick-up/put-down. i would highly recommend reading this book as she addresses how to establish routine when babies are older. i will just share what we when out little one is resisting a nap.
we read a book, close the curtains and hum. place him in his crib. leave the room. as soon as he crys we go back in, pick him up till he stops crying and put him back down. depending on how much he is resisting, i will stay in the room, hidden from his sight. there are occasional times when he crys harder when i'm holding him then when i put him down. in this case i will pick him up put him back down and just put a hand on his back and sing. most of the time the whole thing takes less the minutes.
hope this helps!