(picture for attention)
Very cute - and I love how it is colour coordinated with the pic of you too!
It doesn't look like the usual 4 month regression to be honest as we usually see naps reducing to 40/45 min in length and your DD is still napping well when she gets to sleep. Your A times in the day are fine and I see you've tried altering a little to see if she is better with a little more.
Possibly teething? Teeth on the move (not cutting) can be uncomfortable enough to get in the way of relaxing for sleep even though it is not so painful that they are screaming in the A time, they are easily enough distracted from it. Maybe try some pain meds 20 min before a nap to see if that makes any difference?
Have you introduced solids early? Wondering if it could be gas.
Any reflux? Again LOs can often be distracted from it in the A time and feel the discomfort when it's time to sleep.
Possible growth spurt and she's hungry? You could try a top up feed before nap time if you have time for that?
One thing I found with my DS was that he would cry if he wanted me to put him down for sleep and not keep hold of him. He was tired and just wanted his bed, not to be held sung to or the wind down. Do you think this could be the case? Have your tried putting her down just to see - of course pick up again if it isn't what she is trying to communicate to you.
The last A time before BT looks long. It comes after a CN and really I wouldn't expect her to stay awake as long for a full A time, or at max the full A time, it looks like it's going over. Could you cluster feed, get the bath done earlier and give her that other feed (the 8pm one where she falls asleep) earlier to reduce that last A time? That could help with the NWs.
It may also be that she has some OT build up possibly from the long NWs, possibly from being woken every nap time. Maybe try one nap where she can sleep until she is ready to wake rather than capping at 2hrs just to give her a chance to sleep until she's finished?
There is nothing glaring about your routine (in fact many of us would be very jealous you get those 2 hr naps!) so I've just tried to give a few ideas of things to think about. hope something there might help.