It doesn't have to involve an in-depth discussion of the content. The important thing is to get the editing underway so as to dispel the ugh-field and get into the flow. For this, it should (hopefully) be sufficient to start doing things where any smart scientifically literate person will be able to provide some feedback. For example, devising the best way to organize tables and charts, figuring out how to reword hard-to-parse sentences and paragraphs, etc. You can even make it into a fun exercise where your non-expert collaborator tries to figure things out from the draft while you explain the details that are assumed as background knowledge, and you fix or fill in the text as you go forward. The possibilities are many.

Happy to if needed.

I suffer from something similar on occasion, except my ugh field seems to manifest somewhat differently. I'd be very interested to hear about your progress on this.