To wake a sleeping baby

[HerBluebiro]

Dd is 17 months old. She has one nap a day. Usually 1.5 hours but she needs gentle settling into the second 45 minutes. Usually at midday to 1.30

She's now on nearly 3 hours. Went down later than normal because we went swimming.

If I don't wake her she will never sleep tonight will she?

I would personally let her sleep. Always did with DS naps.

I went with a 7 o'clock bedtime and having been told never let them stay napping after 5 I went with that. Except when they were ill. It wasn't 100% reliable but it seemed to work (DDage 10&8).
If they did overshoot that I generally would wing it though. One odd night doesn't make much difference.