I don't think that she is really being denied anything per se, that would come with being Princess of Wales. Being denied the right to go to the former carrier of that titles memorial service? Not neccessarily a right. In fact, it is not her's or anyone elses for that matter, right to go to a memorial service. She was not granted the right to attend any and all functions when she became Charles wife.
In all other respects she is carrying out the duties prescribed as the spouse of the Prince of Wales, and has chosen to do so under a title that she has the option of making her own. Why would she want the title Princess of Wales since it is so closely tied to Diana's memory?
What else is she being denied?
In any case, I doubt very much that Camilla gives a rats arse about what title she has. She has the most important things, which are the love, respect and support of her husband (as inept as he is at showing it usefully) and her children and step children.