This has been our norm for a few years now, can't remember exactly when it started but we just used to think it was typical toddler behaviour but now she's 7, we're starting to think something can't be right 
Mostly she's fine and happy etc. Sometimes she'll be grumpy and moody but mostly she's okay. Once or twice a week, sometimes not even that, it can be as little as once a month, you tell her it's time for a bed and in the blink of an eye she's transformed into a screeching wild animal who kicks and hits (used to bite me but she's not done it recently) and laughs that she's not going to bed, she's not tired and you can't make her go to bed. She'll run off and hide behind the sofa or under the dining table and won't come out. The crosser you get, the more gigglier she gets
we try our hardest not to lose our tempers with her but it's just so difficult. I've got a bruise on my arm from where she kicked out and caught my forearm with her heel two nights ago.
When she was smaller we'd just pick her up easily and carry her to her room but obviously now she's bigger it's harder and more dangerous trying to carry her upstairs while she's thrashing around. No-one believed us about this until BIL moved in with us and saw it for himself, he was gobsmacked.
The only thing that gets any kind of reaction from her other than laughing, when she's like this, is threatening to take her favourite teddy away, but that just throws her into a complete frenzy, she'll start screaming 'NOOOOOO NOT TEDDY!' So I don't do that but DH can't seem to understand that it makes her worse and makes the already slim chance of her cooperating non-existant 
She's not like this at school, but her teacher is pulling her hair out over DDs refusal to do her schoolwork. She was the model pupil in Reception and Yr2 (she had the same teacher in those years) but in Yr1 and now Yr3 with different teachers, she just refuses to do work and no punishment seems to faze her. She doesn't really have friends at school, I can't remember the last time she was invited to a birthday party and she's never ever been invited to play at someones house. She had a best friend in her class but she moved schools at the beginning of Y3 and DD was devastated and still says she misses her. The teacher has noticed that DD doesn't seem to have a specific group of friends and just seems to drift around various groups at playtimes
She also says she wants to move schools but we're not sure if it would make everything worse or not. It would be easier for us as we have a school that's a 2 minute walk away whereas her school is a 10 minute drive away.
We have a 10 month old who adores her, and in return she adores him. Except when she's in a mood she'll tell him/us that she hates him and that he's a stupid baby. If she's on the sofa he'll stand up and try to grab her she'll push him down, not hard. She just pushes him gently but it's still a push. I tell her off for pushing him but I just get a shrug and glared at in response.
Lately her bad moods are here more regularly and it puts a downer on almost everything nice that we do. She complains that we don't do stuff together anymore, we try our best to each spend time with her without the baby. The other week I took her to a pottery cafe and we had a lovely time just the two of us. As soon as we got home her foul mood appeared and she was horrible for the rest of the day.
We're at our wits end and so's her teacher with the schoolwork. Not really sure what to do because the worst behaviour is at bedtime so no-one sees it and I don't think her bad moods go to school with her, no-one has ever said anything about her being really moody and grumpy. It's like she saves it for at home. Should we speak to the teacher about all of this or what? We always assumed she would grow out of it back when we thought she was just being a toddler but it's clear that's apparently not going to happen.
The morning after one of these bedtime fights, she'll sometimes say she tries to control it but she just can't. She has also said that she had an angel sat on one shoulder, and a devil sat on the other. The devil was telling her to do naughty stuff, the angel was telling her to be good so the devil killed the angel. I wasn't sure whether to be worried about that because it's in an episode of The Simpsons which she watches occasionally so I just assumed she saw it there. She's also said stuff about seeing monsters that follow her everywhere 
Actually seeing all of this written down makes me think we should've gone to see someone about it before now
we just thought we could handle it, that she'd grow out of it etc as she will go ages without one of these bedtime fiascos and we think it's all over, and then it'll happen again...