Consider showing her the book "taking charge of your fertility", which will show her how to chart her temps and know when she is going to be fertile. I would think that this should be madatory reading for all menstruating girls. It teaches you things about your body that every woman should know but were never told. It gives you power over your body.
There are lots of problems with other forms of birth control. Have her do her research.
One thing about the IUD is it doesn't stop you from actually conceiving- it makes you abort the pregnancy. it is in essence, an early abortion.
The problem with the pill is that it doses out all kinds of estrogen. Excess estrogen causes cancer in breast and uterus, and it hurts the thyroid.