It could be a variety of issues that brought this up. Did her behaviour change suddendly or did it get progressively worse over time?

For me depression comes in episodes and tends to have a depth to how down I get. When I was in my teens it was really bad. After the depression I started to develop anxiety too. Panic attacks and the feeling like my chest is tight and the feeling like I need to get away.

If it came on suddenly it could have been a tramatic event. Something that has really shaken her up and she can't deal with it. Physical or sexual assault cam be very tramuatic for someone. If something like that happened it would explain her anxiety about leaving the house. Along with the depression.

My suggestion is to try and be supportive the best you can. Avoid trying to blame her for how she is feeling or put a lot of pressure on her to get over it. Doing this will break trust in you and she will be less likely to talk about what is going on. Try to be non judgemental and supportive. I can imagine that is hard as a parent as you want her to just be happy and get back to living her life.

Meds aren't always helpful. Some medications can make things worse and it is possible she tried some, things got worse and she refused to take them anymore. It can be really agrivating to out some hope in a medicine and then be let down. Medications only do so much and from my experience they work more on the physical symptoms and not so much on the issues that may be troubling you. That is more for therapy.