Dog kneading and holding bed in mouth?

I'm hoping someone has seen this one before! We've had our 5 year old for 1 year, unknown background. She regularly (more than once a day) falls asleep with her dog bed in her mouth, and often kneads it. It seems like a mix of when she's overstimulated, or when she's tired. She is a very anxious girl – the behavior isn't an issue but if it's a comforting/anxiety response, we want to know if there's anything we can do to help her develop additional coping mechanisms for when she's away from her bed. I've seen this behavior a lot in cats, but haven't seen it before in dogs!