It has been two years since N left, Touko was hit really hard by him leaving, she felt it was her fault, she knew it wasn't, so then she felt the urge to make it seem like it was her fault. And she did this by constantly breaking her friendship with her Pokemon, screaming at them, calling them worthless, basically being exactly what N hated.
She wants all the attention from N she can get, you could almost call it an obsession, even though it's more of an interest in his reaction to the new her. Even if it's bad attention, she wants it. She always cries for her own loss of her friend, and now she has a reason to blame herself every opportunity she gets.
She doesn't know why she became an attention-seeking little jerk, she barely remembers the days before she was, when she treated her Pokemon as friends and also treated them with all the respect she could. That's because she's tried her best to forget these days so she doesn't regret the pain she's causing her Pokemon.
At first, she was thinking about releasing her Pokemon, but she figured that would make N happy, so she decided to keep them and just treat them poorly, and she tells herself she's good at it, even though if she hurts one of her Pokemon with her words and even physically, she cries for several hours after, and through that whole time, she apologizes to all of her Pokemon, even though she then acts like it never happened.
If somebody convinces her enough, she may change, just a little, but not a lot. She knows N will probably hate her for what she has become, which is why she wants to stay this way, she likes being hated, she'll be as mean as possible to another person. She doesn't want any friends.
This behavior started when she was a young girl, she was always convinced her father left because he didn't love her, she knew it was true, and if her mother tried to tell her different, she'd scream and cry, calling her 'stupid, worthless mother' and then trying to hurt her. Her mother never disciplined her for this behavior, she is convinced it's perfectly fine.
She's scared of herself, she wants to treat her Pokemon well deep down, but she can't stand seeing anybody happy, she's selfish, if she isn't happy, nobody can be, she tries her best to enforce that by causing other people pain, even going to extremes and putting them in the hospital.
She refers to her Pokemon as 'her toys,' if you try and tell her that they aren't toys, she'll probably get them to attack you and you'll get a permanent spot on the list of people she hates, unless you're N, of course, she wants him to speak to her about how they aren't tools, she'll act as if she appreciates his lectures.