Hello and welcome to Bw forums
I see in your other post on naps that she used to sleep long naps until about 5 wks old - I would guess that the change in napping wasn't so much to do with having "wrong" A times but rather that she came out of her new born sleepy phase and just got harder to get to sleep. Great nights sleeping through though - you'll be the envy of everyone!
With the wake up getting earlier now, this could just be because it seems earlier due to her previously doing particularly long nights, you might have become used to the 13hrs and now that she's doing more like 12 it can seem like something is going off track but can equally be explained by her just getting a bit older and settling into a more reasonable night length. 12hrs is very good.
Clearly you will need to fit naps around school drop off. Are you planning stroller/car/sling naps on the school run and then A time either side or are you hoping for her to stay awake during the school run and nap once home? i would suggest making a rough plan of what you want/need to happen and then work out your times around that. If you need WU to be later you might need to move BT...so think about WU, suitable A time and planned nap time and jot it all down. This is something that you will be able to plan much better than I could as you know your circumstances.
I would also suggest having a think about which naps you;d like to work on - would it be all or would you choose one per day to try to extend? If you are going to pram/car nap during the school run you can allow this one to be a short CN and work on nap 2 being a longer nap for instance - there is no strict rule about exactly what you "have to do" but rather how to make this the best fit possible for everyone concerned. I would suggest starting to sleep train for at least one nap per day in the cot at home and for a long nap.
With regards to A times, I would base your plan for return to school around what LO is able to do for A time, if you haven't been recording your EASY times then begin with 2 days of observation as per the book, and look at what is most likely to be suitable. Then use that as a starting point to jot down where nap 1 is, work back to find out when you need morning WU, and work forward to set out a rough plan (always changeable with LOs though) with one of the naps marked for sleep training.
What do you think?