Hi pinkbunny2012 and welcome 
Were you aware that the nursery were going to be applying for a Statutory Assessment?
As for the comments, at this stage, the Local Authority are deciding whether your DD needs to be assessed for a Statement of Special Educational Needs. Clearly, you want the answer to be 'yes' or she won't get a Statement.
Once they've decided to assess your DD, you'll have to give a much longer contribution to the assessment, but for now, you're just trying to show them that your DD 'probably' needs a Statement.
In terms of what you write, you might want to give a brief timeline of how you got here, and outline her difficulties as you see them.
I'd suggest this:
Paragraph 1: Pregnancy - was it straightforward? Were there complications? Were you aware that your DD would have difficulties? At what stage was she born - early? late? Were you induced? Why?
Newborn phase: Any issues as a new baby?
When you first noticed something was 'not quite right' - who saw her, when did you start seeing professionals, etc. When was she diagnosed with her S&L difficulties, when was she diagnosed with sensory issues, hypermobility, global delay, etc.
Keep these fairly brief, because they're just giving a background.
Then, current day. What causes her difficulty, how far behind is she, what support does she get in preschool, is this enough, or does she still have problems? How do they cope with her, etc.
Stress your concerns about her managing school life, especially if she has a delay in understanding of danger, etc.
Does she put things in her mouth? Does she run off? Does she have a poor sense of danger? Does she have tantrums? Is she toilet trained, or will she need full support, etc.
Anything that you think is relevant - This is your document so you put what you think is important.
When you send it back, send it recorded, signed for, delivery so that you can prove it was received in time.