Lengthening naps is a skill that is learnt. So the more she practices and you help her link sleep cycles, the sooner she will learn.
You want to resettle for every nap, every time. Often it won't work and you'll not manage a resettle, but occasionally it will. The more you do it the more often it will work until linking sleep cycles is a learnt skill and resetting is less and less needed.
A few thinks that make s resettle more likely:
● resettle before baby wakes. This doesn't mean waking baby then resetting. It means catching baby at that very first transition out of deep sleep into light sleep. Resettle at this point any baby goes back into deep sleep without actually waking. Once baby wakes, you've missed your chance because resetting is then very, very unlikely.
The 'tell' for moving from deep to light sleep will be something very small. It might be the face grimiciing, or a limb movement. Certainly if you get to crying or eyes open its too late.
It's essential to be close to baby and pay attention while baby is sleeping, to notice these small signs, so you can resettle as soon as it's needed.
● Have a settling / resetting technique that happens without moving baby from the sleeping position (which you do with patting).
● Avoid over tiredness. More sleep is always better at this age, never limit sleep. Worm to reduce awake time between naps as well as lengthening naps.
The more over tired baby is, the harder to resettle. The more well rested baby is, the easier sleep is to come by.