Hi there.
I think you'll get there with the A time increase. I personally wouldn't be leaving her to try to get herself back off to sleep for an hour though. If her A is too short (and obviously you need to up in increments not one big leap so it's going to take a little time) and she is UT then laying in her cot fussing is a pretty low level stimulation, I'd think it could possibly lead to another UT nap (more like US nap but the results are the same, LO is not tired enough due to low stimulation during the A time). So, if it was me, I'd get her up and do a regular level of stimulation so that your A times are more 'normal'. Otherwise you could be increasing up to a higher A time that she can't handle once she's up and about iyswim.
As for resettling, well my DS has been through various phases of what he prefers for a resettle. There was a time when if I stayed in the room whilst he was going to sleep, or if I tried to resettle mid nap be would go haywire. Trying to resettle a UT (or US) nap is likely not to be received well, more likely you will get loud protests trying to tell you they are not tired
I have also had phases of him being very agreeable to a rub on the back and a key phrase (something like 'it's still sleepy time, go back to sleep').
Another phase of HAVING to be picked up and held for about 30 seconds before being put down again followed by a little rub on the back or a firm hand that he could feel I was there. This was when I was going in mid nap to find him sitting up, if I tried to just lay him down he went MAD, if I picked up and tried to resettle in my arms he would go MAD, there was a very fine line between wanting to be picked up so he knew he had been cuddled and wanting to be in his cot so he could go back to sleep.
Recently I do not need to pick him up and if I do he can get very upset about it. I either just lightly put a hand on his shoulder and tell him 'lie down and go back to sleep' or just the phrase on it's own (sometimes I say the phrase from the next room and I can tell he has laid back down to go to sleep). He now lays himself back down and snuggles to get comfortable and goes back to sleep. he still sometimes wants me to pick him up for a little cuddle though, he might lift his arms when I offer for example.
Now, my LO is older than yours, I don't expect you to follow these methods or for your LO to go through the same phases, but what I'm saying is they do grow and change. As your LO becomes more aware of everything she may respond differently to some shush/pat, a rub, a key phrase, a pick up and resettle down. It's worth a try because sometimes they just do need a bit of extra help to find their way back to dreamland.
I wouldn't use PUPD at all (what I describe above is not PUPD even though it involves picking up), you're right it is a last resort and I think in your case it is more likely to cause stress for both you and LO, esp if she is UT and esp if she doesn't like too much disruption to self settle.
So, I haven't given you a solution here, but perhaps something has helped a little in deciding how to go forward with your LOs naps.
xx
