TBH, I think OX may not be the best place to do a combined degree, but check what specific programmes they offer. I'd be looking at Cambridge for history though (but maybe that's because most of my historian mates are Cantab DPhils).
I know those northern universities reasonably well - any of them would be excellent. Lancaster's worth a look for its remnants of an interdisciplinary first year. It used to be the case that students did a Part One (1st Year) with up to three subjects: their major and 2 others, or the two joint Hons disciplines + one. There's the possibility of shifting programmes between Part one and Part Two (2nd & 3rd Year). York has a pretty stellar English Department, and Durham's HIstory (particularly Medieval) is first rate. Lancaster used to have a specialism in Russian history, and of course is excellent in Medieval history (they have inks with Durham in the area). And Exeter's English department is regularly in the top 5 as is their History department.
Lancaster York & Exeter are all beautiful campus universities in small towns, Durham a bit more in the middle of the town, but still gorgeous. All of these offer a really good student experience because of that - it's a different feel to the big civics - although, for example, History at Birmingham was at or near the top of the last REF, and the Leeds School of English is a fabulous department.
So loads of choice, and really, she can't go wrong wit any of her choices. Wherever she goes, she'll have excellent opportunities for challenging study (if she chooses to rise to the challenge) and a fantastic student experience (if she takes advantage of what's on offer).
That's a great position to be in.