Christina, several months ago Donald (moderator) put me on to the WhiBal card. Basically you take a photo of the card in the SAME light as your subject. When you get into PP you use the eyedropper tool on the card, and it will set the correct WB for the scene you photographed.
In LR you can batch all the photos shot in the same light to set the correct WB.
I believe the web address for the WhiBal card is:
www.whibal.com
or you can Google it. The web site has a video on how to use the card. Apparently it is better to use this than an 18% gray card which is really used in assisting you in setting a proper exposure.
Bruce