[libramunoz]

I hope that you were able to communicate with her.

If you are in this situation again, everybody has given you some very good advice that you should keep handy. One of the things that you can also do is to call the campus police and tell them what you have seen and your concerns about her. Also, go to the Dean of the school or a trusted advisor and talk with them and let them know of your concerns about your sister.
Sometimes, yes, the truth of the matter is that the person may be pissed at you, but you can only let them know that you did it out of love for them and out of the greatest concern about them and their health.
Usually, a person will reach out, but their are the cases when the person says nothing and ends up harming themselves, initially, as a way of calling out for help, but harm (and or death) can come before they can be found.
So ALWAYS, be prepared to call 911 or get the person to the ER to get the help that they are needing (even if they are going to be pissed at you), know that what you did was out of desire to help them.