Hello 
DS is nearly 8wks old, DD is 2.11yrs. DD has been so good with DS and absolutely adored him despite all my fears of her getting jealous etc.
However, the last week or so DD's behaviour has started slipping. I have given her the benefit of doubt over the reason for this - halfway through potty training, a couple of night wakings (nightmares we think) which is very rare for her, lots of bugs going round etc. Late last week though i caught her pulling DS's hair. I was very calm about it and explained that it wasn't a very nice thing to do and would make him sad - left it at that. She has since been quite rough with him, giving his swing a really hard push when he is in it, same with the carseat, wanting to push his buggy and if the break is on trying to pull it over, climbing on him, poking him with things. I don't think she is intending to hurt him as such, more that she gets a rise from me iyswim?
She now throws tantrums when put to bed, wakes up early and sometimes during the night, so is tired and manic all day making the day harder for everyone.
I was wondering if a time out type thing would work? We use a sticker chart for good behaviour and although i try very hard to be calm and rational i have ended up screaming at her a few times 
Any tips/advice/own experiences please?