Concerned about this statement from DD4

[UnlawfulBananaPeeler]

My DD was playing (nothing out of the ordinary just colouring in) and she said
DD-‘Can I tell you something’
Me- Of course
DD- ‘I feel like I need to fight something’
Me- what do you mean?
DD- ‘I just feel like I need to fight and get in a fight. I’m angry’
Me- Do you always feel that way?
DD- ‘only sometimes’

Then just went back to what she was doing .

Is this normal? She’s never said anything like that before. The last couple of weeks she’s become EXTREMELY mean with her little brother (smacking/pulling hair) and had an extremely bad attitude/ smiling when she’s being told off . She’s always been a bit sassy, but she’s really stepped it up a gear .

Is she starting school soon? It's a prime time for boys and girls to act badly- sometimes the adults around them have talked about the Big School stuff so much that they feel anxious and act out.

Can she have a pillow to punch or a stress ball for when she feels angry?

How old is she?
Has anything special happened, that could make her angry/stressed?

Anyway - we all can and do have negative feelings, be in a bad mood, pissed off for now particular reason etc. As grown-ups we tend to hide those feelings, thinking they are bad and we shouldn't be there. I think we also tend to think children shouldn't have them, that they should always be happy and that there is something wrong when a child isn't constantly happy. Well, "negative" feelings are part of our lifes too.
And frankly, I think it's great that your daughter can express her desire verbally, realising that she has the need to do something "bad", instead of just acting on it and not knowing why. It shows a great amount of insight into her own feelings.

She started school today but wasn’t that phased as she went to the pre school next door .
I suppose she must have just been feeling some anxiety but she’s never verbalised it before .

She was really good this morning and then when she came home she was really silly again.

She does seem to be ‘regressing’ with certain things . She’s constantly putting things in her mouth and sucking her fingers(she didn’t even particularly do this as a baby) She’s started to bite and pull hair.
I’ve also noticed she’s having more accidents (been toilet trained solidly for over a year and half) and waking in the night crying.
I wonder if there’s something I’m missing.
The only thing I can think of is her brother is starting her old pre school and she seems a bit sad about it.
Me and her dad also went on a ‘break’ of sorts but we kept it as normal as possible for the children (I.e he put them to bed on his evenings off work while I went out of the way) but the behaviour started after that when he was back home full time. And the accidents started happening a couple of weeks before that.

Maybe she’s picked up on it?

Of course she picked up on that!
Also starting school is a big thing, even if they are not consciously nervous or anxious.

I wouldn't be too worried, especially since it sounds like things have turned out okay between you and their dad.