Make notes of when the meltdowns happen. What happened before . Time of day. See if you can find a pattern.
What does she do when she comes home from school? Can she have some calming /regulating activities ? Drawing, colouring , listening to music, reading etc.
Can you make a safe space for her , not as a punishment but as a safe space to let out her emotions and calm down? She can kick ,scream , punch, throw whatever. Remind her you're there for her when she's ready.
Do a lot of work on her on self regulation. Not only expressing her emotions, but also how her body feels so she's able to identify them and eventually recognise her triggers/getting close to a meltdown herself.
Offer alternatives for what she can do when she "feels" it coming. Ask her what she thinks might help too when she's calm and chatty.
Offer two (acceptable) choices when you need her to do something. Like would you like the red top or the blue one? Will you brush your teeth now or after your story?
Look at social stories and make some specific to her.
Try and end requests with a thank you.
Praise the positive behaviours and be specific. So rather than good girl, say "thank you for waiting your turn patiently " or "well done for recognising you were getting frustrated and taking a break".
Catch her being good, even if it seems silly or something she's supposed to do anyway.
Give her a chance to "fix" her mistakes. Not for violence , but other outbursts.
Give her constant, real reminders. We're having dinner in 10 minutes. We're having dinner in 5 minutes, so finish off your drawing. We're having dinner in 2 minutes , put your stuff away. It's dinner time now, come sit down.
Sit her down and come up with some house rules and consequences for breaking them. Give her reminders /warnings about this and a chance to modify her behaviour.
Try and end requests with a thank you. Sounds daft but it works about 80% of the time. Wash your hands, thank you.
Try not to say no too many times in a row and rephrase your no's /redirect. Instead of no running , say walk please. Instead of no sweets, delay and say after dinner, or offer an alternative . Instead of no telly, say oh let's do Lego instead , then you can watch some telly after.
Clear expectations, a routine as much as you can and narrate the day as much as you can. When we get home you can have your quiet time , then we're reading your book.During quiet time or once it's over , we're reading your book, then we'll make dinner. And so on.
Be consistent.
Very importantly, pick your battles.
It's exhausting and time consuming and none of it it's a quick fix, but it should help to keep the days calmer and hopefully less negative.