Hi again, thank you for replying back to me.
Having read your information your daughter sounds like a bright child and may be experiencing problems expressing an emotion such as jealousy or anger with regard to smaller children.
For example if she sees you giving attention to her younger brother and gritting her teeth, this would demonstrate a jealous reaction. If she has a toy taken away from her or perhaps a puzzle spoilt by a younger child then this is frustration and anger.
You need to observe her and try to pinpoint when she is gritting. She may be using this as a form of control to stop herself lashing out at a child younger then her as she knows she will get into trouble. Perhaps keep an informal diary of when it occurs help you see the cause each time.
When you see her gritting perhaps talk to her quietly and calmly and ask her "whats the matter darling, is there something I can help you with?" If she is good at communicating she may be able to tell you. For example "that boy took my toy".
If you can identify the problem area you can then deal with the cause and effect. For example if it is anger through a younger child breaking toys or interfering in a puzzle, suggest she does it at a table where they cant reach.
If it is jealous behavior of a younger sibling talk to her about how much you love her, let her know you love spending time with her and playing with her but also that you need to look after her brother. Then introduce a role of big sister helper, ger her involved in games with the little one and helping you bath and change him. This will make her feel important and valued and the jealous behavior should subside.
The other thing to try is the distraction technique, as soon as you see her gritting, take her attention away to another situation, "come on darling lets go and read a story or choose a puzzle". So you are immediately changing her thought process to something new.
It may also be worth finding some activities which talk about different emotions, simple games about feelings will help her process and understand if she is having feelings that she may be having trouble expressing.
This is a good book available from amazon and suitable for her age : How Do You Feel (Understanding Myself Series) [Library Binding] Child's World (Firm) (Author), Childs World Editors (Author), Frances Hook.
I hope this has been of some use to you. I look forward to assisting you further.