Melissa - could be teething, but waking repeatedly at night crying but resettling fairly quickly, and short naps of 1h 15 can also be a sign of OT. It could be she is building up a bit of OT from the transition. I would just keep a close eye on her, offer EBT's if she short naps (like I see you are doing today) & hopefully she will get through it. She seems to be coping really well with it so far.
Gemma - (((hugs))) I'm sorry I don't have much advice but I have total sympathy & understanding. O is also really struggling with the long A times & has been incredibly tired. We kept him up til 8pm for the clocks changing & he was up the next day at 4.45am. I have persevered with the 5hr A time, 1 nap & EBT every day & we have been doing this for 15 days now. We are getting shortish naps of around 1.5hrs, occasionally a touch more, but he is absolutely shattered, waking repeatedly in the evening & from 3/4am onwards & getting around 10hrs at night which is very low for him. Today he was at his grandma's & was due to nap at 10.30am, but he practically fell asleep in his highchair at 9am so she put him straight to bed. He slept 30mins (OT nap for him) & so he ended up having 2 naps today. And he was soooo much happier tonight when I came home from work so I know its what he needed. Yes it is best to stay with the routine as much as possible so their bodyclocks get used to it, but there are many, many mums on here who will tell you they needed to throw in the odd 2 nap day to stop OT from building up during the transition. If you really want to stay with the 1 nap (as I do agree its less confusing to their bodyclocks) then I would really advocate an earlier BT. You might find he will get less OT that way, & this will hopefully stop the EW.
WRT an emergency plan for childminder, if she felt he really needed it, could she give him a really short nap of say 10-15mins max at 9.30/10am & then do his nap at around 12.30? At least that way he has a bridging nap to get him through to his usual naptime, AND you get to keep the long nap at the same time as he takes it at home? Ooh or if you could do it at 10am then it might just nudge his nap a touch later to 1 ish & then that would mean you could pick him up ok? Just a thought.