All went well, we showed her it earlier in the day, when we collapsed the cot. She enjoyed sitting on the bed reading with mummy.
Tonight, I said it's bed time, and she actually said "yes" the first time I mentioned it. Then she said "cot" and I told her "no, you're in the big girls bed tonight". She asked for Spencer and Miss Hoolie (soft toys), and waved and said "bye mummy".
I'm just waiting for the big bang as she falls out - it's quite a high divan. (I have put the cot mattress down on the floor, in case, still undecided about a guard).