Here's why:
* Metaphor: A metaphor is a figure of speech that directly compares two unlike things without using "like" or "as." It asserts that one thing *is* another thing to highlight a shared quality.
* Comparison: The sentence compares the woman's hair to ebony (a dark, dense wood).
* Shared Quality: The shared quality is the shine and darkness of the hair and the wood. The hair isn't literally made of ebony, but the metaphor emphasizes its lustrous and dark appearance.
* "as": While the sentence does use "as," it's still a metaphor because it equates the hair's shine and darkness *to* the properties of ebony, rather than simply saying it's *like* ebony.
Contrast with a simile:
If the sentence were "Her hair is *like* shiny ebony," it would be a simile because it uses "like" to draw the comparison.
Therefore, "Her hair is as shiny ebony" is indeed a metaphor.