Hi there!
4mo is a tricky age for naps as there is a lot going on developmentally that can disrupt sleep, and a sleep regression, which usually is related to change in sleep patterns and more difficulty transitioning between sleep cycles. I remember struggling with short naps with both of mine at this age.
It helps that she can SS for naps, that usualky helps LOs learn to transition when they're ready to. Could the grumpiness be developmental? Is she working in new skills? Rolling?
Any chance she's unwell and that's causing tiredness and grumpiness? If either developmental or illness, she should settle back to her happy self & better naps in a week or 2.
If not...
One thing to try could be a top up feed before the nap? I tried this with my DD around the same age as she was stretching to a 2hr A time but able to go long enough between feeds to get a good nap. I tried a top up around 30 mins before the nap.
How close to 5mo is she and how long has she been doing a 2hr A time? Just wondering whether another possibility might be trying an A time increase before the 2nd nap? In case the tiredness is UT/OT?
The short first nap looks OK to me, some LOs never take a long first nap, my DS was like that and could do a full A time after only 35-40 mins and never slept longer for his first nap.