Anxious parent: how to protect the child?

I'm married to a great, loving mother to our children. She is, however, very anxious (clinically diagnosed for many years). Our 3-year-old daughter is now showing signs of being anxious in daily life and it's disturbing to witness it in one so young. My wife clearly got it from her own mother and the environment in her home, and I would really like to break this circle and protect my daughter.

While my wife is naturally bossy and that's no problem as I can just address the issue quietly, when she is worried about something that is urgent (and there's much last minute drama in this world) she can be loud and tempestuous and this creates tension that is clearly being soaked up by the little one. Fear is the default in so many responses and all sorts of implausible scenarios are invoked to justify various responses (she seems to read an inordinate number of Daily Mail shock stories as some sort of feed for anxiety)

How can I as husband and father help to make our home a calmer place, and how can she as mother curtail her anxiety so that our little one avoids it?