AAARGH!! I feel your frustration my lovely. Can I be honest, I don't know. It doesn't really make sense to me. Your LO is turning out to be a bit of a mystery. TBH R can be like that sometimes. I tend to have to resort to a set plan with a couple of contingencies. So my general rules are when I can't work it out:
1. Ask myself, is the sleep issue bothering me more than her? If so, post to check there's nothing I've missed and stay as consistent with the routine as R will allow.
2. Is there something bothering R - teeth, pre-school, any change that might have an effect
3. Set the nap time (with the contingency of +/- 15mins (no more or less) to allow for EW or decent WU)
4. Set BT (with a contingency of allowing BT up to 30minutes earlier in the case of a rubbish nap or 6pm whatever the WU time if No nap)
5. Keep my fingers crossed that whatever is causes the crazy shenanigans passes before I loose my mind
No real advice. Just some food for thought