How can you tell if someone is on ecstasy every day?

I think my friend may be using it but I'm not sure. She comes to school every day and acts very... strange. She didn't before this year. So, other than dilated pupils, how can I tell if someone is using ecstasy every day? PLEASE give a detailed response. The more I know the better time I will have determining if she's using. What would she act like?

: http://alcoholdrugstreatment.info/how-can-you-tell-if-someone-is-on-ecstasy-every-day