I agree with you completely. Princess Grace was a remarkable woman with many admirable qualities, however, it's unreasonable (not to mention unfair) to hold Charlene Wittstock to any "standard" that one might feel is worthy of her predecessor. Both Grace and Charlene deserve far better than that. They should both be admired and appreciated based upon their own merits.
To answer your question regarding how Charlene can make her mark on Monaco, it is my humble and respectful opinion to say at this point, she should keep her eyes and ears open and her mouth shut. I reached this conclusion based upon the recent interview that she granted the British gossip magazine, Tatler. In it, she made several disparaging remarks about her personal life (specifically as it relates to certain of her insecurities of life in Monaco) and her future hopes (modernizing Monaco by opening up coffee houses and high-end shoe stores). I mean seriously, if someone asked her what a princess does and that was the most intelligent response she could come up with (especially with the track record of highly accomplished royals - both past and present), it would be to Charlene's benefit (and Monaco's as well), to give back the ring and return to South Africa, post-haste.
In the interview, she referred to being the subject of jealousy and other what-nots. She bemoans the lack of friendship, the adjustment to protocol and the fact that the people of Monaco don't take to her South African humor. Having studied no fewer than a dozen books (and an untold number of exclusive magazine articles) on Princess Grace, I must say that Miss Wittstock's public airing of her woes (and at such a time as this, the pre-marital period) is most un-princesslike.
I don't know how Charlene feels or what she's going through, but if experience is indeed a teacher, she should take a lesson from her predecessor. While Grace readily admitted, on several ocassions, that she hadn't had it easy in her role as princess and that her life was never the fairy-tale the world wanted it to be, she stopped short of disrespecting her husband or their people by publicly assaulting them or her enemies (and yes, she had several). Grace may very well have spoken of her ills (and the people who inflicted them), but she did so tactfully and in a most discreet manner which allowed her to vent her frustrations while maintaining her dignity... and allowing others to do the same.
I'm unclear on what form of training that Charlene is currently taking to prepare her for her future role, but my advice to her would be this - with all the free time you have running off at the mouth to gossip mags (which can only diminish your standing in the eyes of your new homeland), it would be wise that you devote your time and efforts to mastering the culture and language of Monaco not only through books, but by going out and engaging effortlessly with your people. You should also carefully study the personal lives and reigns of successful royal wives (i.e. Princess Grace; Queen Alexandra, consort of Edward VII of Great Britain; and Queen Elizabeth the Queen Mother) and learn well their lessons.
Take note Charlene, dignity and discretion are 2 ingredients that can make for a very successful princess. History has shown us (through Prince Charles, Princess Diana and others) that on odds, absolutely no good can come of this. You are a beautiful and accomplished woman in your own right, build upon these with other strengths which I'm sure you possess. They will serve you well for carving out an indelible image of your own. One in which you, and the world, can be most proud of.