If there is any trusted person IRL with whom you can talk, I think that would be a good idea. Bounce things off of friends. Also, I think it would be good for you to get paper and pen and write down things. Like write out what you are worried you might hear. Write out possible responses you might like to make to criticisms that might be made of you.

From having been in situations that I think may have been somewhat like yours, I would also say practice thinking about not"over-responding." It can be less stressful if you foresee this as not about getting into a debate with the line-supervisor. You don't have to agree, or disagree, with what is said to you. It is a good idea to listen respectfully. I know that, in these type situations, I used to have a tendency to get really hyper-emotional and that did me no good at all. You might even take a little note pad to the meeting with you. (You really have to feel out the vibes, but it might not be as weird as I know it might sound.) You could note down what is being said to you, so that you can remember and look at it after. Also, I think people are more careful about what they say, if they see that you are making a little record of it, even though it's just a few notes. Then, after the meeting is over, you can look at your notes by yourself and see just what is the issue. And you can show your notes to trusted friends and say "Does this sound reasonable?"

Insecurity about your means of livelihood is bound to be awfully stressful. I've been through it repeatedly. It's worse than people generally acknowledge. I truly believe that job loss can cause PTSD. I don't say that to scare you, but to recognize that what you are going through is truly hard.