dictionary.reference.com/browse/cutie+pie

This is how she got the name, not that video. It's a very common nickname for girls.

exactly, also i think her account is older than that video

Meh me using common sense :

Felix uses Pewdiepie as name , and Marzia is making a spinoff with that name.
Since girls like the word "cute" apparantly, but cutepie would sound lame.
So she made it : Cutiepie, which sounds almost the same as pewdiepie -V

Pew-die-pie
cu-tie-pie

He mentioned in an older video that the fans had commented and given her that name, so yeah, you are all wrong. :3

(At least that's what I'd like to think.)

Pretty much right there