I would begin by teaching her some basic parts of speech.  Every sentence at minimum needs a verb, a subject and an object.  For example, "I (subject) love (verb) ice cream (object)!"  You might be able to modify the game found at http://www.education.com/activity/article/play_word_bags_third/ to fit your 1st grader's understanding of parts of speech.

Another idea is a pacing board.  To make this, make a strip of plain  paper (3-4" wide and 1-1.5' long).  Evenly space 3-6 stickers across the paper.  (You might try making different strips with 3 stickers, 4 stickers, 5 stickers, etc.)  When she speaks a sentence, have her touch a sticker for each word she speaks.  Ask her questions and tell her how many words she needs to use to form her answer.  For example, ask, "What is your favorite food?  Tell me your answer using 5 words."  She would respond, "My favorite food is chicken," etc.

Hope these help!