I would turn up at the appointment with a prepared list of issues that are causing you problems with statistics, OP. You're at PhD level and good enough to be there obviously. You don't need hand-holding to get a list together ready for your appointment, you can do that in your sleep.
It's up to you, your supervisor is throwing you a lifeline here. They obviously believe in your ability to get this done. You're having a blip at the moment, I understand that. There's no need for it to sabotage your work up to this point, particularly when this is important to you.
I'm not going to send you hugs and kisses because I don't think they help, they're a sop. You have a real issue here - your PhD - and it's bugging you so I'm focused on that.
Now, what do you want to get from your appointment tomorrow? Could you add that to your list so that you don't forget anything in the moment?
Can you pinpoint the area of stats that you're struggling with so much? I doesn't sound like my area (probability) so I'm possibly unfamiliar with the issues that you're stuck with. I think, if you could pin these down ready for your meeting, it would be incredibly helpful for your supervisor/the specialist who is coming in especially to see you. It would also give you some focus right now.
I think you can do this, OP. You can get your PhD. The portents are good - instead of your supervisor saying to you, "You're right, this isn't for you, you're not up to this level.", they've actually told you to get some specialist help on the stats element because that's what they think you need. That's positive and you should be proud that your work is of the required standard, that people aren't being dismissive of your efforts so far.
I won't tell you to pull yourself together but I will tell you to try to get your thoughts into a cohesive and logical list of points ready for tomorrow.
You can do this if you want to.