Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.

Clinical Depression is generally considered TREATABLE. I don't think yours is being treated .... effectively.
Either get medicated, which I totally recommend, or learn to present a false front and quell the urges to let it all hang out in front of her.
Make sure you have down time away from your girl where you can do all your crying. But when you're with her: cut it out. Just cut it out. Slap that smile on. Stitch it in place. Ask about HER day and her life. Arrange playdates. If she has friends playing she doesn't even have to notice you're a mess.
You don't have to be happy fun times mummy but you can be quiet, reserved, good natured mummy. you don't have to be the life and soul of the party, but you do have to get her breakfast ready and put up the christmas tree.
If you don't like the way you are making her live, don't make her live that way.
Would you feel guilty if you had cancer and the children had to deal with that? It's no different. A mental illness is a disease. They need to understand that!
Best of luck!