Thanks everyone. I suspected she would go off the rails a bit with not seeing Grandma for a while, but assumed it would be at home rather than at nursery!
She has changed key carer from one she got on brilliantly with as well, and I imagine being apart from her friends has thrown her a bit too - especially when she can't see her Grandma and can't see her friends either! Fortunately one of them is still in the nursery area with her for one day a week, and yesterday both of them spent some time in the preschool where there was no problem. She definitely talks even more when she's been in the preschool and is keen to do more at home afterwards, so if it's a regular thing it might help.
Ah well, trying the 'happy jar' technique of getting a marble at the end of the day if I get good reports, so we'll see if it works...
DD has attended the same nursery since she was 7 months old and generally loves it. She's often praised for being really inclusive with the other children and 'looking out' for the new ones. However, for the last two weeks I've heard nothing at pick up time other than bad things. She's been in time-out every single day for not listening to her carers (though when asked she knows exactly what has been said, so not a hearing problem), then for snatching from other children and yesterday for telling younger ones that they weren't allowed to play with her. Everyone usually remarks on how easygoing she is, so I don't know what's triggering it. At home she's being lovely, doing things the first time I ask, saying please and thank you without being prompted, and the only thing that has changed is that she's constantly putting her toys in time-out.
Her grandmother - who she's very close to - is in hospital at the moment and I've had to explain that we can't see Grandma as she's very sick at the moment and we're not sure when she'll be well enough for visitors . Her two closest friends have moved up to the next room and she doesn't see them as much, so there has been a lot for her to deal with.
It's a bit difficult to tackle the behaviour when she does the exact opposite at home; I'm trying the 'that's brilliant! you did that the first time I asked you to and it makes me really happy. It would make everyone at nursery happy if you did the same thing there too, wouldn't it?" but no idea if that will work - hasn't so far