Let's say she needs 15h of sleep per 24h. At home she probably can do 3h nap when at nursery it's going to be 1-1.5h. So let's say nap will somehow compensate, she can also sleep in on no nursery days, I guess to catch up... Hopefully.
But in general I would go for 6pm bedtime as a rule on both nursery and home days. With a no nap or 40min one in the nursery I would do even 5pm bedtime or whatever you can go for. And when she starts to sleep at night without NW, you can go for any kind of later BT. What do you think? Is it even feasible?
What I am trying to figure out is how to give her 15h of sleep as an average when 3 days a week (only 3 days yes?) she sleeps right now 11h at night and average 1h at naps (12h vs 15h before). Do you have some logs how much she slept in last weeks after the nursery started?