13 year old granddaughter diagnosed Autistic

Hi. She was diagnosed about 5 months ago - very clever, but hated breaks/lunch hours and said she couldn't/didn't know what to say to people. She now is having lessons from home. She is football mad, been in a team - a good player - for about 6 years, but own worse critic even though she's good. Had tournament two Sundays ago, then wouldn't come out of her room, and hasn't been training since, even though football is her world; wouldn't talk, absolutely horrible to her brother and sister - doing things to deliberately annoy them; parents try to talk to her and it's - get out etc. She's obviously very sad and unhappy, and my daughter/son in law just don't know how to help as she just won't tell them what the problem is. Does any one PLEASE have any advice. Thank you. It's so sad.