So what's up with Ellie's voice?

I honestly haven't found another character like this. Is she supposed to sound like that or is the voice actor just not good at their job?

What I mean is every time she talks it seems forced. Half the time she seems extremely animated when there's no reason to be and the other half of the time when she sould be speaking up it seems like she's just plainly reading the script for the first time.

Is it just me, or has anyone else noticed this as well?