we have had a phase like this, also during the transition. I eventually worked out that having daddy home at the weekend is really exciting; when it's just mummy here in the week I keep activity really low key and quiet for the 45 mins or so before her nap; when daddy's here it's all fun and craziness right up till nap time- she was just too wired and keyed up to sleep! I would ask your nanny what kind of activities she is doing leading up till nap time and try to do the same. The more boring it is to be awake, the better Sophie goes off to sleep!