I feel for you, you must so want to see her calm and happy. A couple of ideas - Bach Flowers Rescue Remedy. A link is attached as there are various types depending on what qualities you want from it. I put a few drops in their drinking water and a couple around their ears and paws when they are freaked out, or I know they will be. I haven't needed to use it much, as my two have grown into pretty confident cats, but just a suggestion for you to try.
http://www.bachflower.com/rescue-remedy ... ch-flower/Another idea - your nervous cat may feel better to be kept in a safe room whilst you have visitors, if that is possible. It means she doesn't practice interacting with others, and she might miss out on whatever fun is to be had - but overall she may feel better to be in a closed room with hiding places so she can just tuck herself away till the all clear.
Good luck