I would personally go for set nap and set bedtime. That way she can vary her nap length if she needs more or less sleep, and doesn't lose out on the extra sleep again by having bedtime moved. It's worked really well for both of mine that way and when you start getting bedtime resistance you can slowly cap the nap to keep to the set bedtime. When she was in the early months on one nap DD used to make up for bad sleep at nursery with huge naps of 3h at home, and would still go to bed at the same time as usual ie after a very short A. I think really with toddlers it is more about setting times so their body clocks know what is going on, and leaving the adjusting up to them x