You probably would know if your daughter has been less cheerful or less talkative than normal, lately. If you have already seen some signs of depression, then talk with her about this. Let her know you understand if she has things bothering her and you can talk with her about it.
You even might try taking her to the mall or to lunch, so you have an easier time speaking to her.
Don't put off talking to her.
Begin some open dialog an let her know that you can help her by talking, or she could go either to her own doctor or to someone else for a bit of counselling, if it help. If she knows you have experienced things like this, she may be more likely to open up to you.