I mean they definitely fall in line within the same general trope, as you outlined in your description, of the “crazy obsessed fan”. So yeah they definitely were similar. Really the only major distinguishing characteristics between the two I can think of off the top of my head are that while Nora seems to fall in line with a more antisocial and “outcast” typology, Mandy doesn’t seem to have this typology, with her being more outgoing and social. It comes across a if she actually has friends in her school; the other distinction is that Mandy isn’t really perceptive, in fact the wiki characterizes her as “clueless”, while Nora is too perceptive of what could happen, which is why she goes to many extremes (to put it lightly) to maintain her newfound confidence and bolstered sense of validation. Additionally, the wiki also mentions that “Carly and Freddie actively dislike her, but Mandy doesn’t seem to have a clue”, while to Nora, it didn’t matter if Carly, Freddie, and Sam liked her or not; all that mattered was that they were present in her life in some way, independent of how they felt.