I would try staying for 20 min after she appears to have melted into the mattress. Babies go through 20 min sleep cycles, and I know our lo would jolt herself awake after 10 and 20 minutes, so we would pat/shh through those jolts before we left the room. She's now 12 weeks, and we no longer have to get her through the jolts, but still have to do pat/shh to calm her and get her to sleep, but usually now it's only 5-10 min. Lots of other moms have encouraged me that daytime sleep really begins to improve between 3-6 mos of age. But I would say try staying for a full 20 min to help her through the jolts and see if that doesn't help her have longer naps.