It depends on whether you're planning a short AM or PM nap. I meant to AP a longer pm nap if you capped the morning nap and are worried about getting another 30 minute pm nap.
We used to get 1.5hr - 2hr nws followed by a 35-40 minute sleep and then tired signs soon after as well. I can't remember exactly what I did, but I do remember I had to keep J up cos too early a nap caused an EW the next day. For jack, those 35-40 minutes of sleep were acting like an early nap and causing EW the next day, no matter what I did for the rest of the day. I'm pretty sure I picked a day where WU time was half bearable (5am or something), and then kept him up til I wanted his morning nap to be, based on a normal WU time. I think I still capped it (might have let him have slightly longer than 30 minutes if he'd do it), then shortened the next A to compensate for the long morning and hoped for a decent nap.
So, assuming the A times you did before which gave you a good nap and night are about that, and that you're aiming for a 6am WU normally, I'd do one day like this:
WU: 4.45 / 5
A: 4hrs 15 - 30
S: 9.15 for 30 minutes if she'll do it.
A: 3hrs 10 (maybe very slightly less if you only get 20 minutes in the morning)
S: 12.55 at the latest. Uncapped.
BT: 7
And then hope for a good night, better WU the next day and then go back to 3hrs 15 , 3hrs 30 and then whatever A you need to get to 7pm BT. It's a bit risky but used to work with Jack. Like I say, resettling an EW used to perpetuate the problem for us, and if you have ds coming up you've got to move BT back some time.
I should also warn you that she'll definitely get tired doing a day like the one above and pushing BT at the same time, but the idea is that she eventually crashes after a decent BT. But if you're not sure then obviously you've got to do what you're comfortable with. Others may have other suggestions....?