I am a huge fan of Love & Logic. When a child realizes he will always have natural or logical consequences for misbehavior, he learns to make better choices & exercise self control. I know it can be tough to come up with an appropriate consequence, which is why parents so often resort to punishment (or lectures), but discipline is much more effective. One thing that L&L stresses is to NOT name what the consequence will be in advance, as some kids decide it's OK. Better to keep them guessing. When DS realized early on that I would always impose a consequence, I rarely had to -- just asking him if he was 'choosing a consequence' was enough to make him stop & consider his choices. And then I didn't have to figure out what the consequence would be.
Will grounding your daughter mean that the rest of the family, especially grandpa, will also be punished? That's not fair or effective. I'm not suggesting your daughter is doing this, but some kids will misbehave precisely to get back at the family or family members, or for the attention. Or they really believe they won't get caught, which does get easier as they age. Your daughter does need to understand that rebuilding your trust will take time & is directly up to her to repair, in addition to any consequence. Punishment lets the miscreant off the hook, so to speak.
I agree that understanding the motivation for the behavior would help you to choose an effective logical consequence, & a therapist might be the quickest way to accomplish this. This isn't about blaming ADHD or a new baby or whatever, but understanding why she thinks the misbehavior is OK. DS was diagnosed early with learning differences & initially tried to make this an excuse, but we refused to let that happen. L&L taught us how to ease up & allow DS much more control over his life while expecting (& getting) good citizenship in our home & community.