Hi G.,
My son is in 1st grade and the teacher has the same complaint. I think its hereditary as my sisters had it too. I think there are two parts to the problem: 1. the child has no real concept of time. They don't understand how long 5 minutes is vs. 10 minutes. 2. the child wants to get it right the first time.
One of the weekly homework items for my son is to write a sentence for each of the 10 words for the week. It takes my son FOREVER to do this. Just write something already! Turns out that he can think of the sentence quickly, but when he tries to write it out he forgets what he was writing. We came up with a plan to help. We go through the words with him, and he tells us the sentence, we write it down on 'our' paper. Then when he's thought of all of the sentences, we read them back to him and he writes them down.
Another thing that helps is to set the kitchen timer. Set the timer to 10 mins. and have her start her work. See how much time is left on the clock when she finishes.
A third thing that helps, if there is time, is to get the homework done before she can play or watch tv. You'll be surprised how fast it gets done.
M.