Well, see
I really need her to have a nap!! (only half joking!).
Yesterday afternoon it was very clear that she was way too tired after not napping, but I have not noticed this for many months... maybe four days in a row of no nap was too much??!
The thing is, she will often look really tired before I put her to bed, but then not nap, so I don't know how I would know to offer it to her! It is nap time at the moment, and she's been in her room for nearly 30min... so far she has not left her room (but she's still awake). So that's an improvement.
No, the girls do not share a room, but with coming out of her room, dd1's talking etc woke dd2 up (right at that 45min light sleep stage I presume). She has not, as yet, actually gone into her sister's room.
The way our house is set up, I can't really see any other way to do this (eg. another place to put her for quiet time), unless she was just downstairs in the family area with me.
Anyway, she is quiet at the moment, maybe she will actually go to sleep! thanks for your advice!