maybe related?
I don't think that she's Destiny. From what we get from Crystalblaze, Destiny was her sister, and they were both part of BrambleClan so I doubt that she'd forget anything about how much clan cats eat, and she said that the gray and brownish red cat was her brother and Destiny and Crystalblaze don't have a brother.
ya mean in the farm? well, you need to talk to hawkfeather until she asks you to find her adopted kits father, then go to fallenclan border and talk to the yellow cat (forgot their name) until they start to repeat things, then talk to hawkfeather and go to the right, then a white arrow will appear, click it and walk to the right until you see the gray cat that appears in the image up here. Talk to her until she starts to repeat and then talk to hawkfeather. And that's how you get the quest "Nightmares"