In reply to GavClayton:
My current winter tights for road riding are Castelli Nanoflex - not windproof, but I've not been cold in them.
Your enemy, as usual, is fit - I'm normally a small or medium, but had to buy large to get these to fit.
Trail riding, I tend to wear bib shorts with baggies over the top and shin/knee armour around Swinley or leg warmers elsewhere - both if really cold.
The Corrente ones here might be the sort of thing she's after:
http://www.chainreactioncycles.com/castelli/tights?f=4294958067
Post edited at 16:23