How exactly do I send a letter to a friend in the hospital?

Apparently, one of my best friends was admitted to the hospital (Parkview) even though I didn't know about it. She had sent me a letter from the hospital, however I don't know what room or anything she is in. And she is in treatment according to her letter, but again I don't know what sort of treatment. It explains why I hadn't heard from her in a couple weeks. So I ask: What method of delivery do I send a letter back to her at the hospital? Any bit of information will be useful. Thank you.