Hi OP. I teach BA and MA Acting at two conservatoire drama schools in London that have been mentioned here. You don't say how old your daughter is. It does sound as though she has not done enough research into this, but if she's only 13 or so it would make sense. If she's nearer her A Levels then I think she needs to undertake this research properly. She is somewhat misguided in her views re her age and naive about the work in 'teen dramas' - sorry to sound unkind. Firstly, an actor's casting is something that is largely determined by their natural looks, and their intrinsic acting 'persona' and will be used by agents to obtain work. It's not something you can 'choose'. I work with one actor who's been incredibly successful in tv and theatre and who has been cast as a young 'working class' teenager in a number of tv dramas and she's now 31. She just has that look. Casting age is often just about looks. Other actors come into their own as they get older and are castable as professionals, parents etc. She can't determine this herself. The work an actor gets offered is down to what the casting directors want and see, alongside the actor's reliability and professionalism.
On a broader note, as others have said, it often takes years to get offered a place at drama school, and the statistics about how many actors are still in work 10 years later are low, even at the top schools. Only 2% of actors make a living and 98% are out of work at any one time. Generally, actors' average earnings are under £10k a year.
If she has the talent / grades to make it to Cambridge, I'd very much recommend aiming for that, joining Footlights and getting involved in as many productions there as possible, including the Edinburgh Fringe shows. The success rates of Footlights actors are significant and the contacts and opportunities the privilege of an Oxbridge education affords can open more doors than an undergraduate degree at drama school. Plus an English degree from Cambridge will offer many opportunities to earn as a jobbing actor- one of my MA graduates did his BA Cambridge and now gets high paying tutoring in between acting jobs- from prestigious clients who will pay a lot for an Oxbridge graduate to tutor their child.
After gaining a degree from Cambridge, if acting is still the goal and she hasn't managed to gain representation through her exposure at Footlights, then a good Acting MA in a small cohort at somewhere like Drama Centre would suit, and would be quick (although intense) to complete and would almost certainly lead to an agent assuming she has the talent.