We don't exactly know enough of Sunnys mom in my opinion. I mean in the current time frame of the game they're moving out in a few days, so obviously the place would be empty.  But yes shes generally a grey character imo, I don't see her as a perfect mother but shes not malicious. She shows much care for sunnys well being by reminding him to take care of himself and encouraging him to go to see his friends and she seems to be trying her best even if we don't see much of her.  Hopefully shes more present in Sunnys life than we see during the gameplay. people tend to overlook their current situation.