There’s pros and cons to both platforms and there’s plenty of people willing to argue each side. I wouldn’t necessarily focus on this as much as trying to find the laptop she’s most physically comfortable typing on. Also for an aspiring writer you may want to look into a screen that’s easy on the eyes over long periods.
Wanted to chime in again with this article I found that may give you some starting points.
https://www.techradar.com/news/the-best-laptop-for-writers