Is there a black and white filter that darkens yellow, specifically blonde hair?

get a different model

Manic Panic.

Dead Link Removed

temporary colour in a wide number of shades.

frank said:

Blue/cyan, but I'm not sure how great that makes her skin look.

The effects of different filters on colours in black and white

http://www.photographymad.com/pages/view/using-coloured-filters-in-black-and-white-photography

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From that link:

A blue filter darkens most colours and is used to reduce contrast

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Maris said:

Temporary hair dye? ...

Click to expand...

My thought as well.

Alternatively, is there a way to use the similarity between her hair color and her skin in a creative way to enhance the photo?

I can't say how it would actually work on a live model but I've copied old family photos from the turn of the century((1900) that were fading out and a light yellow color. Using a blue filter(80A) brought a nice looking negative, brought back what looked to be nearly gone, and the contrast was evident in the negative and hence, the print.