Technically, a married spouse awaiting immigrant visa processing could legally travel here on a visitor visa.
HOWEVER, since she is an intending immigrant, it is entirely likely that she would not be issued a nonimmigrant visa or possibly denied entry even if she was traveling on another existing visa.
Like Jeff pointed out, it also depends on her country and its fraud history.
How would an immigration officer even know she is married and applying for a CR1? Immigration officers know everything…at least it is wise to assume that they do. Attempting to enter by fraudulent means could result in a ban for several years or more.
Ray