The majority (ie 99%) of the jewels in the Queens possession are not personal jewellery. They belong (for want of a better phrase) to the Monarchy which holds them in trust on behalf of the nation.
They are not HMQ's to give in perpetuity to anyone. Any jewellery, for example that Sophie currently has use of, will return to the monarchy on her death. None of it will go automatically to Louise or James' wife.
There are a few items that HMQ could consider as personal - ie the Bouquet brooch given when Charles was born - I think that might go to Anne.
Catherine will have access to all of the collection eventually. I think that she would look wonderful in some of the collars that Queen Mary wore. Strapless dress such as the black velvet and something like.......
http://i49.photobucket.com/albums/f...ewels/Russian20Kokoshnik20Tiara2C20Queen2.jpg
http://i526.photobucket.com/albums/cc343/icrowndk/icrowndk-fr/31991a43.jpg
same as above
http://i30.photobucket.com/albums/c317/WKirkwood/UK/QueenMary6.jpg