Well I'm not saying it's a definite, you will have a better idea than me whether it fits with what you're seeing of her, but I think it's possible that she may be a bit OT before her nap, but then you get her to bed early enough afterwards so that she's not too OT at BT and does a good night. I probably wouldn't make too big a change to start with, even 10-15mins earlier for the nap may be plenty to take the edge of any OT. On the other hand of course it may be that she needs a little more A before her nap! I just suggested OT as you said she seemed tired, also on the two nap days she goes down 1.5h earlier for 1h, so I'd have thought she'd really need more than 1.5h when she's going down that much later, iyswim?
I'd generally recommend going for one short and one long nap when heading towards the 2-1, just because you want them eventually on one long nap, but I know that's not practical for some families. If she struggles to get down for a pm CN after a long nap then you could consider a short UT morning nap instead, aiming for a long afternoon nap, but the timings for that can be tricky to find! On the other hand, you may feel that things are working pretty well at the moment so you'd rather not rock the boat too much
It's quite common for LOs to switch between one and two nap days for a while before finally dropping down to one, my DS for example carried on having two nap days at his CM for a few weeks after he'd dropped to one at home, it helped him to cope with the transition. At some point he started refusing the morning nap altogether but by that time he was ready for one nap every day. HTH?