So, assuming your sister isn't plus-size (because plus-size wool business clothing is much more challenging to find - heck, plus size business clothing in general is a challenge!), I can think of a few places that sell wool clothing appropriate for business: Ann Taylor, Banana Republic, and (if you're looking for an actual suit), Brooks Brothers. She would also likely be able to find wool business clothing at Nordstrom and Saks Fifth Ave. Wool clothing is, of course, more expensive, which is why it's harder to find. One other thing to remind her of - wool comes in a variety of weights - a tropical weight wool is lovely for a summer day, but not so great if your office tends to get cold. And winter-weight wool is awful in the summer, of course. One last hint - if she gets wool coordinates (like a jacket and pants), it's a good idea to always dry clean the items together, so if there is any fading, it is uniform across the pieces.