Are you aware that sustanon is just another name for testosterone? Women should not be taking testosterone, since it is highly androgenic, and masculinization side effects are very common when women use testosterone.
Besides, steroids are not fat burners, and they were never meant for that. If you want something safe and yet effective for fat loss, better consider using the Cardarine GW or SR9009 - they have no side effects, and they are very effective for fat loss.