Why on earth are you worried about contacting her? Why on earth would any of you hide behind the school?
This is a serious issue and you should be telling her mother/father what you have seen straight away. But I would ask them not to reveal to their daughter how they found out, in order to protect your daughter.
Please call them and tell them - this girl needs protection and help.
well done twoteens. Hopefully she has a supportive Mum who will help her get over this and move on in a better direction. You did the right thing and should you start to get flack from anyone (in RL) over this, feel free to PM me x