While this does not change what she has done in the game, as well as prior to games events. Psychosis and eventually repeated dosage of venom, during an already existing mental breakdown, does however explained how Lusamine became so deranged. I already got a theory that the only reason why she snapped back to a more stable mind at the climax of plot all of a sudden is because the mascot legendary DID something to fix the psychosis, as well as the mental effects of the venom (both lunaala and Solgaleo are powerful psychic types, type advantage over poison types to boot).

You know, I think their relationship is one of the most ambiguous things in SM. If she treated her kids like garbage, why would she be different for Guzma? It surprised me that she didn't pull off a "Oh, Guzma, only if there was someone who loved you".

Guzma is also a needy person, I mean, he always feels he need to prove something for everybody. Also, there's the heavy implication that he's an abuse survivor (and unfortunately if a person had an abusive childhood, the probability of them reproduce the behavior as an adult is high if they don't become self-aware enough).

Perhaps in the beginning, Lusamine saw him someone that she could manipulate with treats and faint praises and Guzma blindly obeyed. He just went along with everything she said because she "approved" him, he obeyed her better than her own children. And during this process, Guzma became one of the few lifelines for her sanity.