Butterfli - my suggestions for healthy consequences will differ from some others, but I have been where you are with the frustration of kids misbehaving more than the "average" kids. Teachers told me to basically show them who's boss, but they didnt have training in dealing with depression & mood disorders. Some do of course and some even have personal experience, but not most. So firstly I'd say listen to your own heart and follow what you believe.

From the therapy & many books like "lost at school" & "the Tao of parenting" (my favorites), parenting with thoughtful compassion, listening, advocating for your child, being the calm center in the middle of their storm & a strong loving bond are the keys.

A bond of trust helps them feel secure & believed in. Harsh consequences risk their self esteem in a world that's already dealing enough blows. The bond & trust will make it more likely that she feels safe to come to you with her problems & that you'll be a good listener & not judge her. Isn't there enough judgment out in the pre-teen world? They say to listen and get them talking about even the small boring things & show interest, that when you get them talking about that stuff, the bigger harder stuff will come eventually as well.

Healthy consequences to me are done through effective communication, listening, avoiding humiliation. For example, she got up & dressed for school, I'd say "thank you for that" with a smile. Maybe ask for a hug, they often refuse at that so if you get one, awesome. I'd smile & thank here for that too & say, "I love you so much!" If I got the refusal I'd say, "that's ok, maybe later? I just love ya." (Playfully).

And then later in the day maybe she's extremely moody, maybe she had a rough day, maybe she's had to face peers & teachers who say, "oh are you that girl who was in the mental hospital?" Or sneering, "oh look you decided to show up today? Hmph.." (Those exact things and worse happened to my girl). Sometimes they don't even want to talk, just need time to stew, process, decompress from a bad day. I'd ask if I could help or get her a snack or drink. If she yells to go away, I'd just say "ok I'm here to talk if you change your mind, I just want to help and love you cuz I'm your mom."

Then sometimes they take it out on us because we're the safest place for them to burst out in mean-ness. So lets say she start spewing every name in the book at you & your mom, stay calm as best you can, dont yell back or stoop to 12 yr old level, you can't win at that level against a real 12 yr old lol. Say, "hey please don't be mean to grandma" or "hey that's not ok to treat us that way" and "what can I do to help right now". If she says you can F off or worse, I'd give her some space. If your blood boils like mine does, try to give yourself time to cool down. Maybe ask her if you can try to talk when you're both calmed down? If your mom tries to get in the middle, I tell my mom: please let me do the parenting I've got this, your job is to just be a loving grandma. My mom would sometimes tell me in front of the kids, you cannot let them talk to you like that. I have to take her aside and say, please support my parenting, when you get in the middle it feels like you're undermining my authority, please let me do my job, I know you're trying to help thank you I love but I need to be the voice of discipline. Then with daughter when things are calmer, let her know that wasnt ok, that hurt our feelings, I love you & want to help, but please don't be rude to me & grandma.

I could go on & on because this has been the nightmare of my life for the past 7 years. I hope that might help for starters and some food for thought.