What does it mean when a man calls a woman an “eraser”?
I’ve never heard that. Perhaps he wants her to rub one out?
According to urbandictionary.com, “to erase” means, among other things, to shave with a razor. So it might she shaves her pubic hair. Or she might be a hired killer, or an identity cleaner. Or maybe she just makes him forget.
She needs to get the lead out?
Nipples like pencil erasers?
She’s usually carrying rubbers?
She is a competitive computer builder. (e-racer) 
little light, did you originally encounter this epithet in English or in some other language?
Because the only connection of “eraser” with a possibly derogatory term that I can think of is the French term “tampon”, which can mean “eraser” as in a blackboard eraser, but which in English means a feminine hygiene product.
This is extremely far-fetched but the best I can come up with. Can you give us a little more information about your experience with this usage? Where did you hear/read it, what was the context, and so forth?
The Urban Dictionary has this for the phrase “eraser tips.” This would certainly apply to a woman, though one wouldn’t call the woman an eraser.
So back to the OP, this little light of mine, what was the context and exact wording that raised your question?
You eraser. You brought her.
Eraser? I hardly even know her!