Marissa Benson and Dan Schneider
Looking at how much of a creep that we know Dan Schneider is it makes sense why in his shows he wrote the parents the way that he did it all makes perfect sense right now.
In all of his shows all the parents are either absent, neglectful, uncaring, or wildly incompetent but Marissa Benson was written to be extremely overprotective, but she was seen as a nuisance to Freddie and to everyone because she was perceived as annoying and crazy, but as we know or at least should know from his past and from the big Quiet On Set documentary, he hated the parents that were very involved and worried about their kids and tried to isolate the kids from their parents so of course he wrote Marissa as someone who is a nuisance to the characters and whom Freddie should rid himself of completely.
Plus overprotective parents usually have a reason for their behavior. Maybe in her youth Marissa was neglected by her parents or abused by her father, who maybe physically or sexually abused her as a kid, or maybe Marissa was severely bullied and ignored in school, or sexually assaulted and ignored, or Freddie's father traumatized her, like maybe he abused her or abused Freddie or sexually abused Marissa or Freddie or them both or maybe he left her traumatized and got himself killed or almost got Freddie killed by accident which would explain her overprotective nature.
I chose sexual assault as one of the possibilities considering everything that Dan Schneider did, a man sexually assaulted Drake Bell and his father was trying to protect him and realistically that would understandably make any parent act more overprotective.
With everything we know about the man it really makes you appreciate parents like her, the ones who really care. Plus it allowed her to save the kids from Nora, and considering how famous he was from ICarly it could have been a lot worse, it could have gotten more frequent and a lot scarier and much worse than Nora, so she might have saved his life with her attitude. She was embarrassing but she always tried to protect Freddie, and I have my theories above to try to explain why she was so overprotective, she might be traumatized and may have been preyed upon in her youth and no one ever protected her in her childhood so she always made sure to protect Freddie.