I have some experience in this area.
First, congratulations to your daughter on her GCSE results and good luck in working out what she wants to do. She has nearly a year to decide on this. As others have said, it is not necessary to do a law degree to become a lawyer and vice versa. She should make sure that she wants to do the degree itself, not least because enjoying a degree makes it far easier to succeed at it. There are some good suggestions on this thread ? go to open days, spend time in courts, read some starting law books or books specifically on studying law e.g. ?letters to a law student?. She should also make sure that she?s interested in the Oxford course which is quite philosophical. She can apply for the, very competitive, 4 yr Law and Spanish Law course there without prejudicing her chances for the 3 yr straight law degree (they automatically consider you for 3 yr if you apply for 4 yr unless you say you?re not interested).
On the application and improving her chances. I assume that she has read the faculty website and the links from there. It includes a video of a mock interview and this page has more information including details on open days (note some start applications in January). The best information comes directly from the University as there are often myths and out of date experiences that can put people off. Specifically I wouldn?t worry about trying to impress tutors on open days. Firstly, the law admissions process deliberately re-jigs people to different colleges to ensure similar levels of competition across colleges and to try to get all the best people in. Also, there is a strong emphasis on trying to be as objectively fair as possible so tutors avoid attempts to build relationships beforehand (although will be available at open days for questions). Finally attempts to impress tutors don?t often work (e.g. claiming to be interested in an area that just happens to be their area of interest tends to backfire when the tutor says ?really, reform of land charges is a very specific area, what interests you in it?? etc).
On the admissions process, the decision on whether to interview her will largely be based on achieved and predicted exam performance and on the LNAT. She should obviously make sure that as a top priority she is working as hard as possible at her A-levels as she will need to make sure that her tutors confidently predict her 3 As (the standard offer) to be considered seriously. The LNAT is an exam required by Oxford and several other good universities, more information and practice questions here. The GCSEs will be looked at in the context of her school so don?t be put off by the idea that she has to have straight A*. Many people will have but equally many people get in without those results.
The admissions criteria are on their website here and are application, reasoning ability and communication. Application refers to motivation for the degree not for a career in law so the UCAS personal statement should explain why she is interested in studying the law not (only) in being a lawyer. I wouldn?t worry about not being able to do work experience ? at this stage that is largely a function of who your parents know. Going and sitting at the back of a court is just as good provided that, whatever she does, she can talk about it with intelligence and interest. Given the subjects that she is studying, I?m guessing her communication and understanding of language are very good. Her GCSE?s suggest that Maths and Science are weaker for her. That is not a problem in itself but sometimes it suggests that the person is not so good at logical and concise reasoning. If that is the case the critical thinking course may be good if she can do it at school or elsewhere, practicing tests like the LNAT might also be useful.
You asked what she can do now and this is a huge post already so I won?t say much about interviews but practicing debating (including the listening to the other side bit!) and asking teachers or family friends to have challenging conversations about current events (where they will challenge her views too) would be good and stand her in good stead for law whether she interviews at Oxford or not.
Sorry for the huge post but hope it is helpful. Good luck to her.