Her A times are on the high side, but you're right, she does sound like she might need a little bit more. That being said, I'm thinking you're right -- that you should clock watch and work on 3 hours A time for a few days and see if that helps your naps. You might also find that her A times are inconsistent during the day -- that she might need a longer A time first thing in the morning and a shorter one right before bed (or the other way around, mine always liked their longest A before bed).
Any possibility of discomfort from something like teeth?