Carl, my point is not really about grades, but about engagement. There are lots of opportunities to gain experience and personal skills around subject or other societies. Lots of time to read around your subject, or to attend public (though this might be just a London thing) or parallel lectures, or simply read, go to theatre or whatever. One example is your daughter doing some work for the RSC. It would be a pity if she decided she could not do it because she was too busy growing up.
Yet this seems to be the approach used by others. One of DDs flatmates has announced she won't attend morning lectures because she needs to catch up on sleep following her late nights. Several have expressed surprise that DD has "time" to take part in University sport. Yet sport was part of why DD chose a traditional University. One girl we know has taken a year or so out working as a PR for a smart London nightclub. The mother is not worried. Her daughter is not ready for University, but probably will be one day. Better she earns and gains work experience, than spend a huge amount registering at a University and then not engaging.
In terms of internships, for very competitive careers like law and banking, you probably do need to get your eye on the ball regarding internships quite early. Someone on another thread suggested for law you started with where you want to be, and then work back. So presumably you are aiming for a good internship, the sort that might lead to a training contract, between second and third years, you make sure you are applying with a decent CV. Presumably good first year results and some relevant work experience or volunteering.
Much the same applies to finance type jobs. Larger firms will often take as many as 70% via their internship schemes, and these can be highly competitive with five stage recruitment processes. Only the most technical jobs will be looking for top grades, but I assume all will expect signs of a solid 2.1 plus some roundedness. There are some internships which take students at the end of their first years, but not many. It is worth kids who know what they want to do after University, checking out what might be available and what the application dates are.
Universities may also have talks etc given by potential employers. There were regular "breakfasts" at LSE where you had to wear a suit, bring along a CV and listen to a talk on some aspect of the economy in exchange for a free breakfast. Rumour was that Oxbridge students got dinner! DS invested in a cheap M&S suit but quickly decided, food or no food, that banking was not for him.
Each sector will be different. However engaging fully in your course does no harm. DS is at the point of needing references, and is helped by the fact a very relevant "name" knows who he is and has agreed to write one. When it comes down to it, you need to do well enough at school to keep the doors open for the courses you may want. And you need to do well enough (in a broader sense) at University to keep the doors open for the jobs you may want.