Well when she stands, she does not stand straight like we do, she stands with a curve to her body, putting more weight out to her front that over power her light weight of the so called 3rd leg. She also starts practicing in the episode I showed you, how to maneuver and use it to her advantage.
For example she can use that 3rd leg now to roll under something she is dodgeing, or even jump if you didn't watch the rest of the video.
Adapting to what? She hardly ever leaves her home, if at all, she's never on the battlefield, and she hasn't changed her personality what so ever. So, again, adapting to what and why was the change needed?
For whatever it is, or was, her father created her to be. It is something no one knows, nor does she, which is why as she adapts and changes she has no clue why/how to use her new equipment, but she continues trying them like the fashion (as she did before in the first series with the jet booster hair).
Perhaps she just changed because she wanted to keep trying new things, (as you can see in the video, she was able to utilize more equipment that would not fit her original body before).