Yeah i see it as a coping mechanism for her. Im curious to how bad she was because I believe she always had a crush on nika given how she reacted to the summer incident. I know she lost her friend to him but I feel like that possessiveness she has, has always been there.
Yeah I wonder if we'll get flashbacks of this evil version of Nami during the next session with Amber. and I also have to admit that when I first saw this memory with the eraser and Nami's reaction, my first thought was that she was more jealous of Nika than of Summer. Nami had to experience all this for at least 3 years and her 'bad period' could have been, as you write, getting it out of her system, quoting Nadia and Zara. Turning into a bad kid after losing contact with someone close is generally a theme in the Oceanverse so far, so far we know that it happened to Nika, Nami, Leia and Bella and I won't be surprised that if Summer shows up one day, it will also turn out that she had a period in which she turned into Winter or is even still in it
I disagree, i dont think its anything like that.
I think its 100% obvious that Nami was jealous of Summer taking Nika away from her and not the other way around. She was simply heartbroken and jealous and both are aware of that. Even Amber immediatly figueres it out after hearing about it for 2 seconds.
And i dont think that Nami treated Nika badly, i think its more of a case of her being an bully/asshole towards literally everyone else.
If you look at Nami mimicing Summer's hairstyle now and when she was younger, my guess is that once Summer kissed Nika, Nami felt excluded and tried to emulate Summer. Nami is hard to read, but my guess is that, like in her talk with NIka about Noji and he excluding her, she feels like a third wheel, left out and uninvolved. Her attempts to mimic people and be vivacious are her coping mechanisms. In the coffee flashback, Nami tries to outdo everyone by being more, it's the same thing - she's insecure and tries to be impressive by going all out. Especially when she hulks.
Getting back to the mimic thing - we won't know 100% who Nami was the most jealous of. What I think is she was jealous of their intimacy; she felt left out at the back of the class, the odd one out. I think she was jealous of both.
THe cabin thing, and Nami reporting them missing to the police officer (truant officer?) Laverne could be her not being able to process the idea of them having something together that she wasn't allowed to share. Remember what she says about getting the earring - "you and Summer left me alone and when off somewhere again" or words to that effect. Her biggest fear is being alone.
About possessiveness, the thing is she doesn't want anyone to take Nika away from her, but if you're on her romance path, she is really upset with anyone else showing Nika affection. Her reactions to Bella are very different if Nika kisses Bella or if he interacts with Mila post Nami kiss. So she is very jealous, but also knows that she is desperate enough to take what she is granted.
We also don't know what Nami was like before, the talk after the fourway kiss if you walk with Nami shows that there is a different Nami who is not sugar and spice, that Nia isn't being too sensitive, but Nami can actually be a bitch. We're yet to find out how that all went down, but it'll be revealed - Nika will mention it in therapy at the least.
We also have the fact that Nika was at some point charged as a juvenile. So far we've only seen "happy" flash backs where Nika and Nami first knew Summer, we haven't seen any flashback of the period when Nika was fighting and Nami was mean. Which probably means there's some stuff there that Ocean wants to reveal slowly.
EDIT: Also, how Nami was when she was mean, was part of what made Nika how he is now, that's important to remember - from the talk after the fourway kiss. It's serious enough that he feels he needs therapy for it.