Beyond working for Rare, why was Joanna's actress cast as such?

As my subject line states, I acknowledge she's also a general Rare employee, but primarily simply a composer... I wouldn't expect her to have much formal training within voice acting, and while I suppose casting "one of their own" would be convenient, to my knowledge it's not as if PD was a low budget game, as it was a followup to Goldeneye, so Rare probably could've been pretty discerning if they wanted to. As it's possible her original concept was supposed to have made her American (acknowledging PDZ) it's even stranger to me they'd cast an English actress (or simply woman acknowledging what's been previously stated).

Just so it's not falsely inferred, I'm not trying to imply I dislike Ms. Fischer's acting, in fact I greatly prefer it to her actress within PDZ, and as far as I'm concerned the true Joanna Dark always was, has, and will be English, this is just something I've been curious about for awhile and from what I've read it's never been addressed.