My youngest started extending naps around 5 months and it was established by 6 months. I used the bouncy chair to help baby learn to extend naps, then once established and baby was no longer waking after a short sleep cycle, I moved the longer naps upstairs into the cot.
I feel like I need to 'help' her
I think you probably do. I mean, she will eventually learn how to sleep longer but she could learn sooner if you actively teach her.
This is all tied into learning how to go to sleep too, it is the same skill set. Is she going into the pram awake and falling asleep stationary? On a walk? Being rocked back and fourth in the house?.
If it was me I would work on making sure the 'getting to sleep' was the same as the 'getting back to sleep when not slept long enough'. So I would do dummy, into pram, rock back and fourth indoors. Then at the very first sign of stirring awake (this is not noise, it may be a face scrunch for example) I would repeat dummy re-insert and rock back and fourth.
What happens at bedtime? If she can and does go to sleep in the cot at night (as in going into the cot awake and falling asleep in there, with your reassurance) then you can mirror this for naptimes.
Also - is she over-tired? An over-tired baby is much, much, much harder to get to sleep than a just-tired baby. Likewise an over-tired baby will sleep more fretfully, less deeply and so wake more easily than a just-tired baby. So poor sleep becomes self-perpetuating.
With naps of just 30 minutes, I would be looking at no more than 1 hour awake between one nap and the next to avoid over-tiredness.