How can i encourage my baby to take longer naps?

Use her window: Often with close observation you will find your baby's cues that she is sleepy and in need of a nap. For some its rubbing the eyes, for others its crankiness. You will need to find your baby's individual tell signs. If you are getting her in for a nap at a certain hour and the nap is short, try starting the nap process about 30 minutes earlier. Consistent sleep times are a must.

Sleep: It is important to understand your baby nap routine, if you put her to sleep to soon or too early your baby will have very short naps. Make sure that the baby is in a quiet dark cool and comfortable space and start having routines such as reading or singing, helping find things to teach your baby to sooth herself/himself will help.

Be patient: Many infants will begin to have more regular and longer naps once they are able to crawl or walk. As your baby gets older and more active i suspect that you will find this to be true. I would also add that you should plan on scheduled naps. Most infants are ready for the morning nap 2-3 hours after awakenings. The pm nap usually is after lunch. Note that "sneaky sleep" in the car can ruin a nap.