Thanks everyone... as always the BB community is such a wellspring of advice and experience.

Putting together all of your suggestions it seems like my take-home message should be transition her more gently, expect it to take some time (I can't believe after parenting a baby/ early toddler I forgot that one! ) and don't push ourselves too much while we're doing that. Today I've put some of your ideas into practice.. we did a quick trip of errands at 9am, home by 10 and after some morning tea popped her down for a nap... she went to sleep without a whisper. I also appreciate the ideas about being led by her needs just as I have days when I'm more tired than others.

Can I just add at this point that even with this developmental change in her, it's really hit home just how fast they grow up. I'm happy and excited for her that she's evolving but grieving too that this is one more sign my little 'baby' is a baby no longer No doubt I'm not alone in that sentiment.