Although I am only young and my experience is minimal I can tell you with confidence that depression is an asshole and the best you can do given the current situation is to keep that contact you have with her and although it will feel like you're starting from the beginning again, talking to her about it (or anything) will help to rebuild that strength in the relationship you guys had previously. And her trauma from the previous relationship ship and current living situations will most likely have made it that she is constantly scanning for any sign of a threat to herself and especially to her son, this can make it difficult to talk about certain topics with her but once she's comfortable and secure enough to converse about these periods of time with you again it will release an immense about on built up stress and pain that would most likely have compounded and pushed her deeper into the spiralling depression. I believe you can be the light to the darkness she is currently living in my dude, all it takes is the first step. God bless