OK let me put it another way:
Did the colour not look good - you said it did, you said she was happy when you left - so WHY are you refunding the colour?
If the colour & cut were fine UNTIL she started being awkward and wanted it fixed, then saying she couldn't do any of the times you offered & then pushed for a refund WHY are you now going to refund anything?
It was fine when you left, you've offered to return & fix any issues and she has refused - therefore job done, walk away knowing you did nothing wrong and the client isn't going to be happy whatever you do - mark her as a troublemaker and refuse any further appointment requests & ignore any contact from her.
You don't have to refund her to make her go away, tell her that you did what she asked for., she was happy when you left, you offered to fix an issues she had and she's refused therefore there is nothing more you can do and then sack her as a client. You don't have to refund her anything.