I pushed to 3.75hrs A in the morning and she slept 3hrs.
wow, that is what Z was doing. The days get a touch short if you choose to go for the 1 nap days after a 3hr nap. This is what I did, it may or may not work for you, but Z is touchy and he survived it well.
Keep pushing that first A and let her sleep as long as she likes. If she wakes before 1-1.30pm then offer a 35min CN around 4hrs15 A then a 2hr A to BT.
If she wakes after this time then go for an EBT of a max of 5hrs A.
ie 1 nap day
WU 7 (I never let Z start the day before 6am, if he was up early i discounted it and kept him in his room in the dark.)
Nap 10.45 -1.30 (I gently pushed out this A over time, sometimes I went backwards but or the most part I increased 15mins or so every few weeks)
BT 6pmish (or a bit later if she can handle it)
ie 2 nap day
WU 6
Nap 9.45-12
CN 4.20-4.55
BT 7pm
Z did tack on his nights though so if I did an EBT he wouldnt wake too early. And if he did then I did the CN day. We did a mix for about 2 months. (mostly CN days then eventually he refused them more and more and could sleep through lunchtime)
I really had to stop worrying about 24hour periods too at this stage, and start too look at the week. Now Z is on 1 nap its the same. He sometimes does shorter naps but will give me a better night, or a short nap, short night then long nap, short night then long nap long night
Things do get more consistent though as you get closer to 1 nap.