We are just so fed up at the moment and any advice appreciated 
Technically she isn't my SD as DP and I aren't married but we have been together 8, nearly 9 years so I sort of see her as my SD)
I will try and give as much info as possible without making it too long...
DP and his ex have a 16-year-old daughter together. He left his ex 11 years ago after finding out she was having an affair. From what I've heard, she really dragged out the divorce and didn't want to separate.
When he told his ex about me, she stopped him from seeing SD. She phoned him up constantly, screaming down the phone, emailed his work and harassed his family. She eventually let him see SD again.
One of the times he went to pick up SD, his ex threw herself at him while I was in the car
He left straight away and she stopped contact again - she does this a lot.
My relationship with SD has always been on / off. Sometimes she would come to me for advice about boys and friends at school then other times she would scream at me that I'm a slag and I stole her daddy away from her or that I'm only after his money. The first time she did it, DP really told her off - even I was a bit scared! She told her mum about it and of course she stopped contact again until it was all dropped and forgotten about.
Since then SD has come over, she has trashed my things and I've even caught her stealing from my bag! DP asked her why she hates me so much and she said she would hate anyone he was with, it's not me personally
Whenever he tells SD off, she goes crying to her mum and then her mum gives DP a hard time too. His ex told him to leave me and that would "solve the problem."
DP told SD if she cannot respect me then she cannot come over. I am grateful he's standing up for me but now SD thinks he's choosing me over her so now hates me even more.
SD hasn't been bothering with us recently and she only messages her dad when she wants money for something. We have a much quieter life at the moment but I can see it is breaking DP not seeing her. We are just waiting for the next big drama 