I want to travel to USA with a valid visa (B1). During that time I want to take my wife along with me. What kind of visa does she need to apply for?
If your wife is accompanying you for business reasons, she needs a B1 visa. If she is not participating in your business activities, nor in any other business activities, then she needs a B2 visa. Most US visitor visas are issued as joint B1/B2 visas, so obviously a visa like that would suffice as well.
Why would you think your wife need different visa than you?
If she's one of nationalities that require visa and you plan a short trip, it would be B1/B2 as well.