>>2027958She's pretty easy to explain (if anything, too easy, compared to Murai)--she's a resident demon hunter in a country that's full of (and literally run by) demons, with the protagonist being the badass newcomer. She later becomes damsel in distress and in return for the rescue, pulls Ryu's ass out of the fire (or the gigantic death pit). If you mean as to why she's in DOA, yeah, it's just pure cameo fanservice (with the caveat that they needed to replace the two-tonne heavyweight Nicole, so they decided not to go with a dainty flower).
It's not Shakespeare (though it's not nearly the stupidest thing Tecmo-Koei ever wrote either). She's more or less just a Ryu groupie since then (the only one who's not a ninja).