I think firstly it's fantastic that she's talking to you, so lots of praise for that. Tell her how proud you are of her generally and point out to her and remind of anything positive in her life or anything she's achieved. Be really positive and encouraging with her basically.
She needs to get out of this mindset of waking up and looking for something wrong in the mornings. Without knowing her it's hard to know what the best alternative would be, there are loads of things she could obviously do rather than that though so I'd talk to her about what she could do instead. ie get straight up and put some music on, go for a walk, think of something that she's looking forward to (doesn't have to be happening that day) etc
She needs to know that she really isn't alone in feeling like this. Talk to her about how friendships at secondary school are often a minefield and that things generally get much easier as you get older (as she thinks). Talk to her about anxiety and how normal it is to feel anxious - give some examples from your own life perhaps.
Talk about finding out as much as she can in advance about things to make them seem less stressful (ie researching the open day) how breaking down what she's worried about into smaller chunks if possible might help ie going to observe others doing a new hobby, talking to the person running it when no one else is there to ask about it, joining for part of a session etc. Not putting pressure on herself to always get things right first time, recognise that she is feeling anxious about something, but do it anyway and then feel proud that she has done it despite knowing she was anxious about it (even if it doesn't come off/work out, she tried and that was an achievement).
What does she love/enjoy? What does she want to do at uni? It sounds like she really could do with some hobbies and voluntary work to keep her busy and give her something else to think about apart from school. I would be encouraging her and helping her to find some hobbies and voluntary work that she either just enjoys or that is relevant to what she wants to do. Forget paid work, it's more stress she doesn't need right now, especially if she's struggling to find anything, she'll just feel more of a failure.
I would talk to her about the open day again and ask her if she's feeling anxious because there will be loads of people there she doesn't know, or worried that she won't like it, worried that she'll be put on the spot or asked to do something she doesn't think she can - or all of the above! It's easier to deal with a worry if you can work out what it's about.
Will she be at the open day alone or will you be there too? If you'll be there then reassure her of that, say how much you're looking forward to it and be really positive, remind her of why she wanted to go there in the first place. If she's going alone then tell her she doesn't have to speak to anyone if she doesn't want to but that a lot of the others will be feeling very similar to her. Remind her of why she wants to go and the things she should look out for or things she might want to see.
Is her grandma nearby? You need to start small steps, not with you going away somewhere and her left there. Have her stay for the evening and you pick her up at bedtime, then once she's happy and comfortable with that then have her stay over night while you're nearby and on the end of a phone. Reassure her that she can phone you at any time of the night and that you will be there to talk to her and reassure her.
I have one with ASD OP so all this is very normal to me. She needs a lot of very gentle encouraging/pushing of small steps to enable her to see that she can do it. But take it at her pace because she needs to feel secure. The more secure she feels the more she will be able to achieve. Help her find and take the small steps to get where she needs to be.