Brian Johnson, you asked:
>>> "Can we sort out whether she was called Catherine or Christine? Wasn't that part of the original mistake?"
The answer is no, unfortunately. She has no birth or baptismal records, and she appears with both names on the few records that have survived. Any attempt to bring her line back further is going to fail due to the absolute lack of evidence.
There are all kinds of vanity genealogies written in the late 1800s and early 1900s positing royal background for her (and everyone else in the Hebrides :)), but none can be taken seriously due to no citations.
The curators working on these lines have no choice but to enforce a strict rule requiring primary sources. Without them, all of these lines will stay as-is.
And if there *are* new records to be found, they won't be found on-line -- they'll be buried in forgotten church books in the back of a closet in Stornoway. That's why we have to trust the local experts, who've said quite clearly that the lines are known to the extent they can be.
Building the Scottish side of Trump's ancestry is a futile effort. Build the German side -- loads of records available, loads of opportunities to connect him into other lines.