My youngest 10 year old girl finds it diffcult to sleep

I don't know if anyone can help on here or wether this is the correct place to post but here goes.

Our youngest 10 year old girl has over the last 6 months found it increasingly difficult to get to sleep without knowing exactly where we are going to be in the house and how long it is going to be before we come upstairs.

When the time has lapst when we say we will be upstairs she calls downand we spend the rest of the night up and down stairs trying to settle her until we give in and go up to bed ourselves.

This has resulted in her going to bed later and us going to bed earlier to try and ensure she gains enough sleep.

Her bedtime is now later than her sister who is 2 years older and goes to bed at a time appropriate for her age and is happy to go to bed when she is tired.

The marked difference is that her younger sibling says shes not tired.

She is a very bright girl and is often saying we don't understand though she does not explain herself resulting in her becoming upset.

This often ends in her becoming very argumentative when we are trying to calm her down by not entering into long drawn out conversations. After shouting at us she becoming very opologitic and saying sorry to us both, often in tears which is really distressing for us all.

There seems to be a pattern emerging whereby after washing and tucked up in bed and a story is read to calm her down she seems fine, then becomes restless wanting to know exactly where we are in the house and how soon we're coming to bed. After settling her and we are both down stairs, the calls of she cannot get to sleep start, up stairs we go to try and reason with her, she becomes argumentative, sometimes to do with "you sai you were only going down for a little while and that was 30 mins ago", or something similar, she is then remorsefull, apologetic and when at least one of us is next door to her bedroom, upstairs in bed she settles down to sleep.

This series of events takes between 1-2 hours and his starting to have an effect on our family as to what we can do and impact unfairly on our oldest daughter.

As I menition she is a bright grade A level student doing course work a year above her age, taking this into acount that she is absorbing alot and forums stating of similar cases that some kids do go through stages like this.

She slept happily and soundly for the first 9.5 years hence this being quite a concern.

Is there anyone out there who has had similar issues that could help or give advice as this, although not every night, is becoming far more frequent.

Many thanks in advance