First off.. this is normal. We just have to come up with a strategy to help her handle the transition from one sleep cycle to the next.
1. Take a look at her awake time.. is it too long? Overstimulating before her nap?
2. Excellent with swaddling.. keep this up!
3. How does she fall asleep?
4. Have you gone in at the 30 min. mark? There is an excellent post by Heather 10, I copied it to the Announcement for Short Napping 3-6 months. Take a look at this post, it best describes how to do wake to sleep.