So 8th grade is old enough to appreciate most adult sci fi. The only reason not to would be the sexy stuff but I read some seriously pervy shit in 4th grade and it weren't no thing.

So it's not like she can go horribly wrong... but a lot of the stuff she's going to run across is going to be chauvinist and wooden.

This is the part where I espouse my previously-undisclosed love for Lois McMaster Bujold.

Strong characters, excellently written women, real social problems, and fifteen years before Tyrion Lannister she was writing a far-future space-trader universe as explored by a glass-boned errant dwarf in the space navy.

The first book written is The Warrior's Apprentice. it's got this cover and it's still incredibly awesome.

The first book chronologically is Falling Free, about a space station full of genetically-engineered children with four arms and zero legs created by a corporation as a space-faring race and what they have to do when some putz invents antigravity.

Buy her Warrior's Apprentice. If she likes it, there's 21 more books (I've probably read 6 of them). If she doesn't, that's 21 books she doesn't have to read.