Take advantage of the fact that she wants a Fancy Nancy bedroom and deck it out! For my older son, when he turned 18 months old, we were moving out of the tiny apartment and into our first house. We closed 2 weeks before the month we'd paid for at the apartment was over, so we took advantage of those 2 weeks to clean the house, I bought some stuff on craigslist and set up his first bedroom. His new room was the first room we set up at the house, so he could nap or play in there while I cleaned and set up the rest of the house. I took him to it, and it was his surprise, his present for being a big boy. He was SO proud of that room and his new furniture and "big boy bed" (a toddler bed I got at a great price), so he never gave me any trouble.
For my younger son, we got transferred and moved to a new state, and stayed in a rent house on a 6 month lease until we could find "our house". He was right at 19 months old when we closed on our new home, but since it was a similar situation where we closed before we needed to be out of the rent house. Joseph's room was already the perfect color, and I found awesome bunkbeds and "cowboy stuff" that he helped pick out to decorate his room, and did his room first. Victor, who was still in a crib at the time, was next. I painted his room 2 colors, put the border and valences up, hung up all new decorations, and had his room a great "transportation" room (he helped pick stuff out), and he inherited his big brother's car bed (toddler size). We told him to close his eyes and we guided him to his new room, and made a big deal about his surprise, and it was a gift just for him. He is still, 10 months later, in love with his room and likes to take people in to show them his big boy room and big boy bed.
I say decorate the room how she has requested and make a special deal out of her fancy nancy room, and I bet she'll love it! Let it be a graduation kind of day----she's a big girl. I know that my older son didn't really want to give up his pacifier, but he'd been told that when he turned 3, it would have to go away because he'd be big then. One day we were at Babies R Us getting stuff for the baby (I was pregnant) and he saw me pick up pacifiers. He said "Mine?" and I said no, these are for Baby Victor. He watched me take them to the nursery. He threw his pacifiers away on his own that day, because he didn't want to be a baby. (That was his actions and thought process, not mine)