Here are a couple suggestions.
1. Have your daughter tell you what she wants to write. You can then write it down. If something doesn't make sense, talk with her until she comes up with something that is correct. When you're finished, ask her to copy what you've written carefully.
2. Have her use a word processing program that catches misspelled words. Read it back to her to make sure she's said what she's meant.
3. Try providing reading materials she does understand. I often find easy-to-read information by typing the word kids after my search words. Example: Veteran's Day kids.
4. Talk with her teacher about the problems you see.
I have some ideas:
First, you should find books that she enjoys to read, so ask her what she likes. Then, go to the library or somewhere to find a book for her. Now you should encourage her to set a daily reading schedule, so her reading gets fixed too! But for the writing, when she's done with the book, take her to a word processing program that catches grammar and spelling mistakes. Ask her to write about the book, and take as long as she likes! Tell her just to write a) things about the book b) the characters in the book c) what she wished had happened or what she was glad happened, and finally d) whatever she wants to write! When she's done, you should go over it with her and fix up first the grammar and spelling mistakes and then try to edit and revise the story. Take your time, let her fully understand what you expect and how to fix what she writes about. Repeat this, and slowly work on your last problem, matching what she read to what she writes. Tell her to make them alike, and teach her some easy things to remember about spelling, like 'i before e but not after c!' I was taught that...
Finally, let her have fun with writing sometimes. The key thing to being a good writer is liking what you are doing. If you are not enjoying yourself, then you will not want to write and you will not be good at it because you don't do it. Hope I helped!
thanx guys i will definitely try those suggestions