It's a big change...my son is two and I discovered that he wasn't ready yet, when I had a hard time with him 'freaking' out when I got up once I thought he was asleep. Also tried laying on the floor while he was falling asleep...it just isn't time yet. And, really it's more about me being okay with giving him more time (another few months) than it is about something being wrong with his room, bed or anything else. My son has picked out all his sheets, comforter and the whole nine yards and still refuses to sleep there, so I will wait.
Right now, we do naps in the 'big boy bed' and visit his 'McQueen Bed' before bed and we read a story there before we go to bed in our bed. Since, we co-sleep I'm antcipating more time in the transition process and that's okay with me.
Two is such a transitional age, I'm finding out, and my son's needs change ALL the time. One day he's upset I'm leaving for work and then next he can't wait for me to be out the door or jump into Dad's car for their morning time together. So, just give her time. Make it about her growing up and being a big girl...create a special routine that invovles the bed but, doesn't make the bed something she will be apprehensive about using.
I've seen friends who have made the transition without any issues, and for a while I wondered what was I doing wrong?? And, truly I just have to remind myself everyday to not have any expectations for my son and let him guide me as I guide him on our daily adventures.
Good luck! And, keep up the good work!