How old is your daughter? I've used three tactics for things that must get done soon:
* Put together a customer organizer that leads her through several steps to get where she's doing. For example, brainstorm, pick some favorite ideas, write some isolated sentences about those things, organize the individual sentences, then copy the completed thingy onto the final assignment.
* Have her verbalize what she wants to write to me, I transcript her words onto paper for a "rough draft". Have her use that to write a "final draft" onto her assignment.
* Let her type it on the computer. It's easier for her to change her words and rearrange things in digital format.
For longer-term, we're playing with the writing curriculum "Writing With Ease" at home, which someone had recommended to me elsewhere. It is designed to be done over 4 years if you start with a 1st grader, or you can do it faster if you start older. DD is 9 and finished the first "year" in about 2 months. Since we've only just finished year 1, I can't say how well it will work in the long run.
