The phrase is a variation on "the pleasure will be all mine", which is the commonly used phrase and which I guess you know the meaning of. If you change "mine" for "hers", then the phrase relates to someone else (a female) but still means the same. I've not seen the phrase be used in this way before but there is no reason why it can't be.

Yes, it is a variation of "The pleasure is all mine." When someone changes this to "The pleasure is all hers," or "The pleasure is all yours," they are usually stating implicitly that it is not really a pleasure for the other person involved (and the other person is often the speaker).