I was diagnosed in 2004 and can sympathise with the loss of confidence. Also, being slow and deliberate is a fairly common symptom and can be difficult to come to terms with.
The onset of my symptoms has been slow., but no less life changing. I went through a period of thinking that things would degenerate rapidly, but the progression has slowed down.
I still find it difficult to feel at ease when I am out of my comfort zone, but am determined that this disease will not change the way I live my life. The loss of confidence is very hard to rectify, but just having the support of my family has made all the difference. Knowing that someone is around to support and encourage you is invaluable. I have also made friends with fellow PD patients in my area - not a formal group., just friends supporting each other - again this has been a tremendous help.
It really depends on how confident your wife was before PD, but I think the best way of dealing with it is to face it head-on. ~Do things that make you feel uncomfortable and learn from your reactions.
The main lesson I have learnt with PD is that I am determined not to give in to it - it may be able to cast all sorts of evil symptoms on me like tiredness, muscle spasms, weakness, etc. etc. but it cant take away my desire to fight back.
Driving is of course a different story - you both need to know she is safe, but if she has never been particularly confident then maybe facing this demon may be a step too far at the moment. Concentrate on trying to buiild confidence on the things you know she is good at, If she can believe that she can still cope with the simpler things in life, then that could boost her ability to deal with the harder things.