Don't know why anyone is concerned about what she's singing, she's 8, she's not thinking about the mature social or sexual aspects of what she is singing, she's enjoying the music. I've been singing my mum's Celine Dion, Whitney Houston, George Michael etc since I was far younger than this. Whitney Houston's 'A Few Stolen Moments' is about having an affair! And it didn't make a blind bit of difference to the fact that I was still a child who, having been brought up in a village, was out on a daily basis playing with my friends and having a normal childhood. As far as the vocal chords go, I'm no expert, but I was a good singer at primary school, didn't become a very good singer until age 11 when my vibrato came in and my vocal chords were notably stronger (after puberty was in full swing). So I have no idea how this could affect this little girl, but Christina Aguilera and many other famous singers were belting songs out at Fitri's age and still have the voice now, so I would have thought with the right care she will still have that voice in years to come.
She's incredibly talented, it would be nice if people could just congratulate her and wish her well rather than always displaying concerns. Look how much she loves music, that's all that matters, for someone like her music soothes the soul from the inside out, trust me.

Good luck dear:)))