No personal experience, but teaching social skills at school we'd talk about things like a worry jar/box that you could put all your worries/thoughts in before bed time and they'd be safe til morning. Alternatively, she can tell a special teddy about her worries and teddy can look after them. Then top to toe meditation/imagination, where you imagine yourself in a special place and gradually relax each body part in turn (I'm sure you can Google for a much better explanation!)