She was forced into the experiment. During the Tekken 2 storyline she was captured by Heihachi after failing to assassinate him and was used as a test subject in the "cold sleep" project by Dr. Boskonovich.

RiderFan said:
She was forced into the experiment. During the Tekken 2 storyline she was captured by Heihachi after failing to assassinate him and was used as a test subject in the "cold sleep" project by Dr. Boskonovich.

Uh... his point is that Namco didn't have to write Nina in that manner. No one forced them to subject her to cryostasis to keep her conveniently young after a timeskip.

That said, Namco has no idea how to portray mature characters the way Hideo Kojima usually does.