Writing a song for my friends birthday?

My friend and I have been friends for quite a while. She means the
world to me. Without her I would be like a lost lamb in the night not
knowing where to go or what to do. She is the one that helps me
through my problems. Shes my Sister from another Mistress (: haha
I want to do something REALLY special for her birthday. I want to
write her a song.
I have NO clue how to start though. I mean, I have no clue what to do.
Never wrote a song before.
I know a lot about her. She is such a strong person. She is having
hard times at home and she is always just so happy and spunky and full
of life. She is always there for me when I need her! I get TONS of
emails from her and I keep them all (:
Can anyone help me? Like, what kind of lyrics should there be? Help me
write them sorta!? Ideas would be FABULOUS! (: Thanks everyone!
If you guys need any information or have questions, I'll answer them
to a certain extent for privacy. (: THx again