It therefore does have a different "feel" in comparison to some other universities that would be nearer the bottom of the list
You write this as if it's fact. Are you a student there? Any university in this country which asks for high A level grades will have a higher proportion of independently-educated students, because socio-economic advantage buys educational advantage which generally (theoretically) also buys educational attainment. The Sutton Trust estimates at least one grade at A level ...
I think that this is a situation where either choice will be the right one. They're both excellent universities generally.
Your point here:
DD has been so focused on university entry choosing the right course and place that I don't think either of us had thought much about what happens if she has any hiccups two years into the programme
might be worth thinking about more generally in terms of roaming each university's website for student activities -- look at the Student Union (or equivalent, sometimes it's called a Student Guild) for extra-curricular stuff. Ditto Sports Centre.
Has she had a good look at each Department's website? What are the core compulsory modules each year? How are they assessed? In your DD's case, she might want to consider whether one or other Department eschews a lot of unseen examinations? What sort of options are made available?
Options aren't always available each year -- but a larger Department has more capacity for covering staff absence (research leave, other duties, teaching priorities elsewhere etc etc).
And so on ...
But she's in a great position of having two excellent opportunities. Neither will be a bad choice.
There's always the Phoebe-from-Friends way -- take a choice away: without warning,just say "Well of course you can't go to Exeter/UEA" See what the instinctive gut reaction is.