The trouble with black hair is that is not a colour so you can't change it. Nor does it have a lot of texture unless it is really well lit. It would be much easier to composite blond hair from another picture.
You don’t mention Adjustment Layers which, in my opinion, is how the adjsutments should be applied.
Anyway, apart from what Trevor has said, there are other ways to change a color than Selective Color, a Solid Color Layer set to Blend Mode Color, a Hue/Saturation Layer set to Colorize, …
Try it on full black hair. I don't think any of those options would do a convincing job.
I agree that it is unlikely to yield good results.
If the image was captured with 16bit that might help somewhat.
Does the quality of the picture affect this?
Because the picture was taken with an Iphone. which has an 8 megapixel camera.
An image used as input for an editing process that makes pretty radical changes does need a quality level above and beyond typical, yes.
Apple's portable device cameras are some of the best cameras in that realm yet, but they're still cell phone cameras.
And beyond the image quality, which may not be as good as it needs to be to serve as input to a complex set of edits, shooting a photograph in good, controlled lighting vs. taking a snapshot in whatever lighting can yield pretty different results. That's not to say we don't sometimes get good lighting in everyday situations - sometimes we do get lucky. But think about it: In order to turn dark hair blonde, you need all the hair strands to be individally visible - with no blacked-out areas and plenty of detail. This is achievable with top quality photographic equipment and lighting.