There are pros and cons to both. I studied abroad in mine (rather a long time ago) and loved it, but I now have students who have done both and all have different opinions.
Does DD have an EU passport? Our students used to do some great work placements, but many of the employers won't/can't sponsor visas so that's now a lot more difficult. If she can find a suitable placement, I think it's nice to have some "professional" work experience before graduation. British Council is still fine in terms of visas, and it's a great option for students considering teaching in the future.
Being an exchange student is a once in a lifetime opportunity. She could always get a job abroad after graduating, but this is the only chance to experience (undergraduate) classes somewhere else. Unis in each country operate quite differently and most students find it a very interesting cultural exchange.
Your DD will need to ask her UK university how it will be assessed as everywhere does it differently. Some convert foreign grades into UK grades, others have the year abroad as pass/fail, and others, like @TizerorFizz says, set their own assignments.
For both British Council and uni, some students fully integrate themselves with the locals, while others only seem to talk with other Brits (and maybe the occasional Australian!) A lot of it is down to how much effort the students put in.