Girl SF reader here, weighing in…
Ender’s Game by Orson Scott Card is pretty fun, but if she wants a heroine, she isn’t going to get one there. (I never cared, but some girls do.)
If she is ok with blatant analogy, then the Ships of Earth series (which is also by Orson Scott Card) are very SF-lite with a relatively interesting plotline, with the tech never getting overwhelming.
David Brin is fantastic. Startide Rising is one of the first SF books I ever read, and I loved it. Hard to go wrong with dolphins.
Some of Crichton’s stuff is better than others. *Sphere *was really cool and creepy, with a fun twist that most girls will appreciate. Jurassic Park is silly, but still manages to be a little more interesting than the movie. * The Lost World *may have an edge in that the kids (especially the girl) are a little less horrid there than in Jurassic Park. It’s a little thing, but it still means that I pick up The Lost World more often when I’m going for a brainless re-read.
If she’s really gearing up for the whole SF thing, and doesn’t mind a heavy military angle, then Elizabeth Moon’s Vatta’s War series is good.
Likewise David Weber’s Honor Harrington series. There’s about a million of them to read if she ends up liking them. Honor is a very likeable heroine, and there are telapathic 6-limbed furry catlike creatures. Instant win points. Lots of references and sly nods at political conventions which is also fun to read. Fair warning tho, as the series goes on, the politics get heavier (but you get more 'cats also, which balances things out).
Not precisely SF, but I enjoyed Alas Babylon (yes, mock all you want, but I was young and it was a fun read.) That might be a good starter for something more fun (and more SF) like Fahrenheit or Brave New World or The Handmaid’s Tale.
Finally, I can’t go without commenting on Zelazny. Lord of Light is FANTASTIC, but to be honest, there’s a lot there with the mythology and the layers of tech/magic/miracles and the story peeling back like a mystery. I would recommend starting with the Books of Amber first, and if she likes those, THEN go for Lord of Light and/or Creatures of Light and Darkness.
The best recommendation I have is to find out what she likes to read and find something in the SF field that is similar to that. Finally, she should realize that reading and NOT liking any one SF book doesn’t mean she doesn’t like SF at all - there’s so many different areas and styles that she should try a few out and see if she can find a niche she likes before giving up on the genre as a whole.