In that 2nd video, her Af-Am accent came out in full force. That's one way to distinguish between a biracial and a multigenerationally mixed AA. The former often lack black accents, but not always.
Hair texture is also a big deal. In America, biracials with nappy hair (as opposed to loose curls) are often assumed to be multigenerationally mixed or light-skinned AAs (a lot of people don't know J. Cole is biracial, for example). You have to have curly or wavy hair in order for people to question your ''race''.
This girl appears to be lighter than both of her parents. Certainly not the norm, but it's not unheard of. I would estimate her mother to be about 50 % Euro genetically (not culturally) and her dad to be 20-25% Euro. With that background, it's possible to produce predominantly Euro offspring, which might be the case here. She looks less white in the second video though.