Write out numbers instead of using numerals: three, not 3. (Yes, there are exceptions to this rule, but this example isn’t one of those exceptions.)
Add a comma after three days ago (compound sentence). Change the comma after didn’t come to a period. Add a comma after since (compound sentence). Add a comma after coming.
Change hasn’t to hadn’t.
She had forgotten how long she had been here, but she woke three days ago, and for once, her captor didn’t come. In fact, he hadn’t been here since, and it looked like nobody else was coming, either.