How can I fix the edges of her hair?
I would not even try, you can fix it but it will take a lot of time. Even for me with a lot of Photoshop experience. You would have you rebuild the hair, and delete a lot of it.
Request a better photo, or even just the original one - this one seems to have been tutored in Photoshop.
Find a stock image of a red lady over the white background and use parts of her hair to patch the image you are trying to fix. You will need to grade color a little bit and it will take like 10-15 minutes of work, but certainly doable.
I would do a fuzzy select of the outer hair and then try different blur settings.