Is there any way to help my depressed wife?

My wife was diagnosed with depression many years ago before I met her. At one point long ago she attempted suicide. We have been married for 7 years and in that time it seems like the depression has gradually gotten worse over time. She has been on Zoloft since before I met her as well, and I really can't see what if anything it is doing for her. She is always unhappy, tired, without energy, and doesn't like to leave the house anymore. I do everything that I can to make her happy including calling into work every so often because she wants me to sit on the couch with her and do nothing. I go out of my way each and every day to try to make her happy, but nothing seems to help. She is always tired, and when I do try to talk to her about going to a doctor to see about new treatment options or maybe even go to a therapist, and I even offered to go with her, but that like most of our attempts at conversation lead to her lashing out, and us fighting. She has lost interest in sex which she blames on the Zoloft, even though it never interfered with her libido in the past. We have a daughter who is almost 2, and I don't want her growing up asking, "whats wong with Mommy" her whole life. Besides forcing to go see someone, and by force I mean pick her up kicking and screaming which I don't want, does anyone have any suggestions as to what I could do?