Where do I start.......

my stepdaughter (8) lives with us, she see her tummy mummy once a week 

since having my daughter (3) I've been at home a lot!! SD and I use to get in well. She gets on great with her sister and they play nice together. 

There's been a few issues where she's said things but we know it's her mum that's said it. But it's her emotional state abd her meltdowns, tantrums, outburst I find incredibly hard to deal with. 
She never listens to me and when I ask her to do things there's always a carry on.