so work on a title, a beginning, a middle and an end. then work on building it up in each section.
you can write some with her so you discuss it and then show how it would go in the sections and if you do the writing down bit she can focus her energy on the ideas and developing the story.
I was always rubbish at writing stories, I always wrote too concisely, was always factual, to the point, didn't waste words, often just ended abruptly but then went on to be a sciencey person rather than English so it is probably something that just doesn't come naturally to her skills but it doesn't mean she can't learn to do it. I got good English Language and Lit GCSE results and even thought about doing English A-level. I now write stories for my children so it is possible to develop the skills.
Also it might be worth looking at a children's thesaurus, build an interest in 'exciting' words. Show her how through writing a story SHE has the power to make it as fun, exciting, unusual as she wants. Just practicing some sentences using different words can help build her confidence that HER work is good and interesting to a reader.
For the actual generating of ideas however there's no magic solution other than reading lots and lots of different books and discussing them. Good writers are almost always widely read - they have internalised the different types of story structure and have a 'feel' for creating their own plots.
As well as the books she's reading at school and home, I'd choose something that's a bit beyond her ability and read it to her, or get stories on CD or download so she gets a wide experience.
I think writing a short story is quite a skill! It will come with practise though. Have you tried story cubes? These are prompts that should be incorporated into a story and this works well for DS. You could try limiting the number of sentences, so 3 for intro, 4 for middle and 3 for end etc. Usborne do a good book on story writing too.
She is in a mixed year group, y3/4 dd is y3. In y1 for home work she undertook lots of do what ever on x topics, mostly tipical, not much spelling numeracy was gsmes etc, but dd lovedvlooking in books snd on the internet for informatuon she could copy, replicate and write about.
Y2 home work was spelling, very restrictive and a bit of a task for dd, mostly Phoenix, words ending in..., words benign with, split sounds etc and make sentences. I'm sure yr2 for dd was very much revision and sats training, her work was rarely differentiated and she pledged along I feel.
Homework today in y3 is again very innovative and dd could wait to get it done, how ever I noticed to my surprise she struggled. It was spellings very basic and I must admit when I first looked at it I felt it would be robotic and uninspiring as it was last year, however although the spellings were basic the task for the higher group was to creat a story with each word contained using connectives and more than 3 punctuational.. Dd struggled, she gave me ideas, after a clear beginning and plot she got lost. She then wanted to just do the bottom group task, write a scentence for rah word. I encouraged her to give it a go, but she really struggled to come up with a story. I was surprised and felt given the in y1 she would have breaded it.
I gave her a few ideas but she could not grap that she needed a middle, beginning a d end with a c,ear p.ot that could incorporate all the words. She waffled. Didn't grasp my ideas etc.
Her story was factual, non descriptive and she struggled to bring it to an end. How can I develop this without dictating a story to her?