I agree with others here that this girl’s problem isn’t really discipline.
I mean…if you has a psycho hosebeast mom and every time you got to visit your loveable dad he pawned you off on his girlfriend, wouldn’t that drive you insane? No matter how awesome the girlfriend was I would feel totally rejected by my dad.
And she’s got six grandparents that love her and buy her stuff. Does she have 6 grandparents to take her out to do fun things? Six grandparents to hug her and read to her and visit with her? Or just six grandparents who fill her emotional void with material things?
I’ve read about dads on this board and elsewhere who are admirable “weekend daddies” - they bust their asses to be able to spend time with their kids whenever they have the chance. These dads also have to deal with their own mature needs - juggling their love lives while still being there for their kids.
Since your boyfriend doesn’t have to juggle his lovelife and his daddy life (he’s got a girlfriend AND a nannny!) he’s really getting off easy isn’t he? You and his daughter are the ones suffering.
Ask him how things would be working out for him if you weren’t in his life. Don’t present it as an ultimatium, but see what he says. If he says “I’d get a babysitter on the weekends” ask if/how he could afford it if you weren’t living with him. If he says he’d rearrange his schedule to be with her, ask him why he can’t do that now. Get him to see how his actions are affecting both you and his daughter.
He’s really taking advantage of you and neglecting his daughter, so it’s obvious why you and she are completely tense about it. Your relationship with her won’t get better until she feels better. And she won’t feel better until her dad grows up.