what time are you putting her down for a nap? she may not be tired enough and needs more A time? like any new developmental thing they learn, it will be something they want to practice and if it were me, i would lay her down and walk out, repeat, repeat and repeat and she will learn its nap time. during the day you could try some activity time in the cot, giving her lots of practice and i taught my dd how to sit down from a standing position by encouraging her to go down by guiding her hands down the cot bars.
Also you mentioned you let your dd CIO, the bw condones this method of sleep training as Tracy believed it broke the trust between the parent and child.
pu/pd doesn't work for everyone but you don't have to pick her up every time. i would simply put her down, say your sleepy phase and leav.
let me know how you go
