You guys are silly. Season 2 ended with a shot of her entering the doorway we see here standing in front of at the end of A World Between Worlds. Not only that, she went back through the same portal she was pulled out of which was set to Malachor at the time of season 2.

That was the answer to the mystery of her fate at the end of Season 2. She was pulled out of time but then returned shortly after.

What she did in the time since then is the actual mystery. I would guess studying on Malachor and elsewhere.