How do you reduce a cream sauce? My wife made a cream based sauce last night and the recipe said to "reduce" it.
The cream sauce was comprised of some white wine, couple cups of heavy cream and chicken broth (my wife substituted water for the broth)

I looked up how to reduce a sauce, and it basically said to heat it up til most of the liquid evaporates and the sauce gets thicker.  Makes sense, but the website I was on said that the liquid should simmer on low heat while reducing.  I was doing this but it was taking forever and was still very thin (~30 minutes).  I cranked up the heat to high and that sped things up, but I'm wondering what the proper way to do it is.

Should she not have added water?  Was there something else we missed? Or does it really take that long to reduce a cream sauce?
The simple answer is: You reduce a cream sauce the same way you reduce any other sauce, by simmering it until a certain amount of liquid is gone, just like the instructions said.  You have to be careful about temperature though, because milk (or cream) can burn at high temperatures, and then your sauce is ruined.  You should keep it to a low or at most medium simmer.

Cream sauces normally tend to thicken extremely fast, so the long cooking time is almost certainly due to watering it down.  I don't think the water was necessary at all; the chicken broth was probably for flavouring, and although "broth" is a somewhat nebulous term, one would normally expect a broth to contain at least some amount of gelatin, which will cause the sauce to thicken substantially when it cools if you reduce it a lot.  Water doesn't, so you've added no flavour and thinned out the sauce.

Basically, you (or your wife) added water for no other purpose than to try to evaporate it later.  Water generally doesn't go in a cream sauce.  If you don't have chicken broth or can't use it, I would either substitute more wine or just leave it out completely.  Usually the only time you substitute water for broth is if it's actually the base of your sauce.