14 Year old daughter

Hi All

We are in the middle of the diagnoses for autism for my 14 year old daughter. 

i am struggling with her at the minute - it feels like it flares up every few months, then it settles for a bit then we are back there. 

Most of the issues are social - for example todays drama is she wrote something nasty about a swim mate and then someone she thought was a friend told the swim mate. But her humour and moods are half the issue - she said she wanted to drown the swim mate. She didn’t mean and she doesn’t know why she said it other then the swim mate got on her nerves. She’s always either completely high and happy or completely low and depressed. That’s the same with the things she says and does - this team mate annoyed her so she’s at the extreme end of not liking her. It’s really hard to get her to empathise that she would be upset if it was the other way round. 

I try talking to her but it’s in one ear out the other - I feel. 
Then if I try to put a punishment in place nothing works as she doesn’t care about anything enough - will hand over phone, iPad, drawing stuff. Didn’t care I haven’t let her go swimming. 

I’m downstairs upset and she’s fine upstairs. 

 Tired of the constant battle to get her to understand.