When you are selecting hair, it can be very difficult to get clean slections on the edges!
Here are some ways to fix that:
1) Use the lasso tool to loosely select the subject
2) Click on Select and Refine > Click select subject
3) Click refine hair
4) Click on Decontaminate colors
1) select your subject
2)mask it
3) Filter > other > minimum
4) CLick: Perserve > select roundness and adjsut the pixels until it is a clean selection