The problem with any kind of severe depression is that the sufferer can't make herself do what she needs to do. Even worse is when the sufferer blames herself over something with which she has no control, like L is doing. None of it is her fault any more than if she had the flu and couldn't function.
It doesn't sound like she is getting the help she needs (probably because she is trying to keep it a secret). This needs to be viewed just like any other illness, and get treated. No one would say, I'm so ashamed I have pneumonia, so I'm not going to get help. Perhaps if you and G presented it to her that way, she could see the depression differently enough to seek treatment (or improved treatment). She needs to do it for herself and her baby.
Hang in there!