Hi, there.  Have you talked to your daughter at all about your observations?  I don't know what your relationship is like with her, so what you say to her will depend on that.  If she admits to being depressed and is willing to see her doctor, I would encourage her to go, or to see a psychologist and get an evaluation.  A regular family doctor can hand out pills but not much else and is not an expert about these medications.  A psychiatrist has much more expertise in this area and some do therapy, as well.

Because she is an adult, there isn't really much you can do other than be supportive and encourage her to get help.  One of my sons is 35 and has been depressed off and on since he was about 12 and even now, I worry about him not taking his medication or seeing his doctor.  What I do is ask him how he's doing, make suggestions and let it be because I've discovered if I get at all pushy about it, he just digs his heels in.  Maybe this isn't the case with your daughter and it will be easier for you to get her to get some help.  Let us know how things go and feel free to write in any time - the people on this site are good listeners!