Seth has been doing the same and he's a few days older than your DD1.

I just persevere and some days it will take 20 mins to get him to sleep other days 45 mins. But I keep persisting because I know he NEEDS his sleep. My daughter did this at this age, and continued to have naps (after this phase) till about kinder age, and even now will ask for a rest if she's tired. So I think for us perseverance was the key, but obviously everyone is different.