Hiya Amy. So definitely sounds like the later nap is helping her wakeup time - yay! WRT BT I'd say yes 6.30pm is probably too early now the nap starts at 11.45am. When we did this with O it was at this point that we started to push BT later too. After a 2hr nap we did 5hrs A time to BT, so with an 11.45-1.45 nap that would be 6.45pm BT. Once the nap got to 12pm then BT was 7pm & so on.
However, O was 16 months when we did this, & since then his A times have jumped & now at 19months he is UT at BT with a 5hr A after a 2hr nap - this may be why C took a long time to settle yesterday. So she might actually need a longer A to BT. This is where it gets a bit tricky though, as the longer A time means a longer day which can lead to OT. This is why we have started capping O's nap at 1.5hrs, as he started waking early again with the 2hr nap, so we are now trying
Up: 7am
Nap: 1-2.30
BT: 7.30
WRT the mid nap WU's - yes they do sound like OT & it is probably down to you pushing the nap later - it really did make O quite OT too. I know you would like to keep a consistent BT & you can if you dare & just try & ride it out, but I have to say if O only slept 1hr I'd do EBT or he'd be shattered. Probably at 6, definitely no later than 6.30pm.
HTH.x