It sounds very good to me. Only change I would make is replace 'white lights in it' with 'white highlights', making the sentence: "She had an extremely bad complexion and pale yellow hair with white highlights, exactly the colour of molasses taffy that has been pulled until it glistens." Edit: Google "recipes for molasses taffy" would be my suggestion if you after what colour her hair is, if it's like molasses taffy.

It’s a weak description in my opinion. Taffy is not known for having well-known standardized colors.

Her hair is golden or light brown, as far as I know.

"Taffy" is a kind of candy. It comes in blocks, like this: https://www.crosbys.com/wp-content/uploads/2014/02/Toffee.jpg The candy is stretchy, though, so if you pull it, it will stretch out. You can continue to roll it together and stretch it out again, or twist it, like this: https://www.crosbys.com/wp-content/uploads/2016/09/molasses-pull-taffy-5sm-194x150.jpg It becomes more shiny when you pull it or twist it. So her hair is the color of taffy, with white highlights that make it look shiny. (As Greg says, the text should probably say "highlights," not "lights.")