To write a poem for your daughter, first decide what you want the poem to focus on, then jot down your thoughts that fall within that focus. Pick the form you want your poem to take and start playing with words and phrases to make them fit within the desired form.
There are many possibilities for the focus of your poem. You may want to list your daughter's good qualities and character traits. You could write about your feelings for your daughter. Your wishes and hopes as a parent are also a possible subject. Memories and stories would work too.
Poems don't have to rhyme, but if you decide you want your poem to rhyme, start pairing up phrases and, using a rhyming dictionary if necessary, substitute main words for others that rhyme, while maneuvering your sentence structure into a desirable rhythm. Repeat the poem out loud as you write, listening for the rhythm of syllables within phrases.
If your poem is free verse, meaning it does not rhyme or have any specific rhythm, the emotion behind your words will be the focus of your poem.
It will take many revisions to get words, meanings, rhythm and rhyme all aligned into one flowing, meaningful poem.