I think a lot of people are attracted to the "making a difference" and vocational careers and I was the same.
After being a teacher, support worker and something similar to an ISVA, I did a complete u-turn and retrained in a STEM career. I have never been happier, even though I always thought I'd have to have a "front line helping" job to get any job satisfaction.
I wouldn't discourage her as she may love it (lots of replies already from people who do love it and she may be one of them) but I'd discuss what exactly draws her to it and see she can get in touch and speak with anyone working in the role already.
Make sure she has a realistic idea of what it is like. I think a lot of people want to work with babies/children without realising how much of the job is actually working with parents.
When she imagines doing the job, what is she imagining? Is she imagining comforting quiet, afraid Timmy and helping him get better? Is it like a movie where she's the one person who can get him to have his injection?
That's fine but does this mental picture also consider Timmy's mum who is at her absolute wits end and terrified, who criticises everything she does, demands a different nurse because of something completely random, complains about things outside of anyone's control and blames her when he's not getting better?
It's one thing to sympathise with why Timmy's mum is doing that, but to have that day in and day out does require a certain thick skin that not everyone has (such as me, it turned out). Then on top of that the stressed colleagues, workplace bullying, blame culture etc that often come with working in the NHS which is bursting at the seams.
I can't speak specifically for nursing but I would want her to go in with her eyes open. Work experience, volunteering or part time work would be really good, especially in an intensive, demanding role with patients/clients who can be angry and within a system at it's limits.
If she is able to get some experience and finds she responds to that type of environment in a positive way then great. Go for it. If not she can rethink. I really wish back then I had more awareness of the person I actually am and what makes me happy rather than getting a job for the person I wished I was. It's hard to know exactly who you are when you're young and so I think the best way is to get stuck in as a soon as possible in as many different places as possible. Care homes, schools, hospitals etc. it'll be great for her CV too.