Honestly, I wouldn't focus on her condition or trying to give uplifting advice. Its too easy to get it wrong, however well meaning you are.
When I've been inpatient I really enjoyed phone calls. Often the whole unit would come running when the phone rang, hoping it was for them. Letters are great too. Keep it light, ask how she's doing, talk about whats going on in your life. Tell about something cute your kid did, or something that you did that day. I'd just let the conversation flow naturally. Care packages are also wonderful, especially since its a long stay. I'd wait a week or so, and then ASK what she would like, what she's allowed etc. Generally there are restrictions on what can be brought onto the unit, and it varies from place to place. There are the obvious things- like no sharps, but I've also seen some you wouldn't think of- no stuffed animals, no toiletries, no food. Other places have allowed food, toiletries and stuffed animals, so its best to ask her for some guidelines. And, sometimes you discover you need something you wouldn't have thought of! For instance, I once had to ask for some new shirts because I hadn't foreseen needing this specific type of shirt when I packed- but once there it was obviously a necessity.
As a general idea, most places require the use of phone cards or quarters for patients to call out, and they tend to be very in demand. She would probably appreciate a phone card, and a nice note. Reading material also tends to be in short supply and is generally allowed, so long as its clean. If they allow it, some art supplies might be appreciated - crayons or colored pencils, maybe a coloring book- mandalas are popular to color in a lot of these places.