Now the only thing we need to figure out is HD, BAB and saves so she can progress normally. At lvl 1 she won't be imbalanced with her mental stats, as she won't be able to use them that much. She is a Small creature that can use it's claw attack. That's it. If she had class levels then the attributes would be bad. Plus I'm keeping consistent with her write up from the sourcebook, and even giving her the Dex bonus at lvl 2.
Past level 5 she will start taking class levels, at which point her SLAs and improved DR will be scaled off those right?
Regarding HD, BAB and saves, Outsiders are d8, get full bab and 3 good saves. Maybe progress like that, or is it too much? Note she still doesn't have weapon proficiensies or spells or anything of that nature.
[sblock=Unholy Scion progression]Level 1: Claw Attack, Familial Charm, Instant Knowledge, Int +6, Wis +2, Cha +4, DR 1/good and magic, Resistances (acid, cold, electricity, fire) 1
Level 2: Charm Person 3/day, Dex +2, Fast Healing 1, DR 2/good and magic,
Resistances (acid, cold, electricity, fire) 2
Level 3: Darkvision 60 ft., Cha to AC, Fast Healing 2, DR 3/good and magic, Resistances (acid, cold, electricity, fire) 3
Level 4: Unholy Strike, Desecrate 1/day, Fast Healing 3, DR 4/good and magic, Resistances (acid, cold, electricity, fire) 4
Level 5: Immunity to poison and mind-affecting spells and abilities, Spell resistance (HD + 10 (maximum 35)), Enervation 1/day, protection from good 3/day, Fast Healing 4, DR 5/good and magic, Resistances (acid, cold, electricity, fire) 5[/sblock]