It's hard to answer this without knowing more details B. Is there a 'mood music' that she wants more? From what you have written in the past, it seems like you have a friendly and warm relationship. I have that with my friends - male and female - and am not looking for mmore. I know it is different, as you have had a past relationship and have kids, but it may be that you are her safe zone because of this. In fact, I think you are her safe zone. But she is not yours at this time, and that involves some sacrifice from you. How long will you be able to do that? In your shoes, I would want to know the same.
That's the difficulty of looking at things through an MLC lens I suppose - one way or another, we blame the depression. We hope they will come out of 'it'. Subconsciously, we may be waiting for something. I am not saying your W didn't have a major episode, but you can only really deal with what's in front of you now. I know this is not a particularly helpful answer. I guess only you can decide if you wish to keep the ship steady and wait for something more definite from your W.
Hypothetically, how do you think she would react if you decided to date?