Is that asleep by 11.40 and 6.30, or PD at those times?
If she is usually asleep at 11.30 then it's to be asleep by 11.40 instead, just an extra 10 (or 15) mins A time. Same at BT, asleep at 6.30pm.
It looks like she is getting two sleep cycles in the nap of 1hr 20 which is not enough for her, this is also what my DS did when UT. Adding an extra bit of time on could help her be just that bit more tired, tired enough to transition to the third cycle and get 2hrs instead of 1hr 20. The 2hrs made all the difference for us, it helps get through enough hours in the day and he was properly rested.
I'm cautious to suggest adding a lot of A on though as you've only been at 11.30 for a short while...but sometimes you just have to guess and try, if she can get that third sleep cycle then it's worth it.
She doesn't cry out but chat and then roll around sucking her thumb seemingly trying to resettle. If I go in to her it's game over! Jumps up and runs around the cot.
This sounds like UT behaviour. She is somewhat tired and kind of wants to go back to sleep but can't and then prefers to get up and play rather than keep trying. If my guess is right the extra 10 mins or so will prevent her waking at all and then she doesn't have to try to get back to sleep.
If there are any suggestions of how to resettle I can definitely try...
If she is usually able to settle herself from an OT nap and just go back to sleep then you don't need to resettle.
With mine, when he dropped to one nap, I had to "tell" him to sleep as he had horrible 20 min naps and woke every 20 mins throughout his 2hr nap. He would have been happier (for a short while)if I'd got him up but knowing he wouldn't go for a second nap later in the day meant I absolutely had to stick it out and "make" him sleep. it wasn't particularly pretty during that phase. I then worked out I could W2S every 20 mins and he didn't fully wake and scream, the W2S with my hand on him helped him to resettle/stay asleep. I only went in for about 1-2 min and back out the room again, it was very fast but vital at that time. If her naps doesn't lengthen with the slightly later nap you could try this, creep in when she is still asleep and put a hand on her or be ready, hovering with your hand just above her for the first sign of transition/waking and pat/rub/stroke/sooth her through to the next cycle. You'd probably need to go in at 1hr 30 or 1hr 35 to be ready and so as not to disturb her.