Well, based on the information they game, Wesker "walked out" when Jake was born. Jake then had to become a mercenary to support his mom financially.
From this, I don't think Jake's mom has ever been mentioned before this.
It can't be Jill because Jake was already born before Wesker captured Jill (Also, neither Wesker or Jill were infected with Uroboros. Jill never was, and Wesker infected himself right before he died).
I don't think it could be Ada because she was never in financial need...