Hi,
i'm no expert on wpw, i've only recently been diagnosed myself. But when I had an attack it was better for me to be sitting down, it usually made my heart slow down, and get back to it's normal rate. I've had this for about eight years now, and I don't ever remember having an attack while sitting down, I was always doing something.
I'd assume then that driving would be ok. Doesn't she take medication to control her heart rate? I've been taking some for three months now, and I can get as excited and active as I like and I don't get a hint of an attack.
I've just been looking at a forum website that answers many questions. You might want to look at it. I vaugely remember seeing something about driving, but as I don't drive I ignored it.
You can find it at:
http://This link has been removed/healthtopics/svt.Html
i hope that helps.