Sometimes she feels so at home on Earth that she forgets she's actually an alien.
Sure this body feels alien, but it's also the most at home she's been in centuries.
Her forgetfulness is quickly rectified though, through the harsh glare one of the other inhabitants of the cave throws at her.
She is the intruder here - she has no place in their home, invading their place of safety after she and her kind have taken their planet. That is what they're thinking.
And no matter how at home she feels, she knows they are right. She is the alien here, no matter how much like home it feels.