Hi Dianne, I think there are a number of reasons why a baby's poo can be green. It may be the formula is doing it to her. It may be something else. I Googled and found this info about b'fed babies:

If your baby's stools are nearly always green and if he is not gaining weight well even though your milk supply seems fine, then it could be that he is getting too much foremilk and not enough hindmilk. As the foremilk is more dilute, with more lactose and less calories, it stimulates your baby's digestive tract to move the milk along too fast producing green, often explosive, nappies!
I also found this:

Consistently green stools could also be a warning that your baby is sensitive to something. Is he on any medication? If not, could he be sensitive to any medicines that you are taking, like iron supplements or antibiotics? Very occasionally, a baby can become sensitive to something in his mother's diet which is passed to him through her breastmilk
Sorry I can't give you a definite answer, hopefully someone more knowlegable will come in and help you!