I have preface this by saying I'm not certain of any specific case which may have prompted Gregory VII to include that -- perhaps he was thinking of a particular example, or perhaps he was just being thorough and covering his bases. However, there is at least one notable example that Gregory may have had in mind: Agnes, Duchess of Aquitaine. After her husband the Duke died, she ruled Aquitaine as regent for her son for several years, and later continued to be quite politically influential. After she had married Geoffrey, Count of Anjou, she and her husband did exercise powerful influence in the election of Pope Clement II in 1046, a fairly important milestone in the ongoing Investiture Controversy concerned with whether the power to appoint church officials lay with the Church alone, or if secular rulers had authority in that area as well.

In any case, there were certainly women in 11th century Europe who wielded political power, sometimes the soft/unofficial power as the wife of the ruler, but sometimes officially as regent for their minor child as heir. I believe it was less common, but in certain situations a woman could also inherit a title and rule in her own right, such as the County of Bigorre which had several sovereign countesses.

And while it's a century too late for the time period of Gregory VII, I can't resist mentioning the fabulously fascinating Eleanor of Aquitaine, who in addition to holding the title of Duchess of Aquitaine in her own right, was also Queen of France, then Queen of England by her marriages, and was probably the most powerful woman in Europe for much of the 12th century.