I have a 4 1/2 month old and I think most small babies don't nap long. From what I've read, 3 hour cycles for wake, eat, play, sleep are pretty common.
I've also learned too that the swing is great for lulling him into sleeping longer. However for us, at this time, that means he's up more at night then. He simply can't seem to get all the calories he needs if he takes those longer naps (I'm talking more than 2 hrs here). In the swing, he can nap up to three hours! Mostly, he's a catnapper. The first nap to develop is the afternoon one. So keep trying to get her down by 1pm to teach her "it's afternoon naptime".
I'd rather have him awake when I'm awake. Otherwise he wakes every three hours on the dot at night.
Don't worry. She'll start sleeping longer soon enough. I know the swing/car are tempting now.