Earlier quoted context omitted.
I had a coworker who went through this. My bosses were very gracious. She was on leave for some time, purely for mental health reasons. And I’m sure returning to work with her job intact was a major comfort. Our direct boss at the time would meet with her for lunch occasionally until she felt well enough to come back. I’m willing to bet it was the best way it could have gone for her in light of what she experienced.…
I am happy to hear that she is beaming. But, from personal experience, I would not assume that she is anything like "over" losing the other child.
My own problems with seasonal / occasional depression have resembled something of a bell curve- not bad at first, then really bad, then not very bad. The threat of depression never really goes away, but the likelihood of having bad days generally dies down over time, especially if the gap from what you were missing (IE child, job, spouse, sibling, family, pets) gets filled by something else.