I thought she didn't. I thought that vader killed her, and she was brought back when erza bridger changed time in the world between worlds.

Uber

The same thing Grievous did when he flew out the Invisible Hand: Call a space taxi

Somehow, Ahsoka escaped Malachor.

^^^

But even after being saved she still emerged back at Malachor. Question is how she got off planet.

I mean it looks like she didn’t die but she went into the wreckage area in the episode of Worlds Between Worlds. So she probably found her own way off probably whatever ship The Eighth Brother arrived on

She was saved by Ezra in the WBW

She was pulled away and put back by Ezra in S4 through the WBW. You can even see her silhouette leaving Malachor in the S2 finale.