Her history is sad. She (and her parents) were starved until Lexi was a few months of age. From the way she behaves, it looks like she was also abused in other ways.
She was taken in by a lovely couple, who got her used to people, children, cats and other dogs (though she's scared of Buffy).
She's quite small - I don't think she'll get much bigger.
My humans have decided that over the next few days, we're fattening her up, and slowly introducing her to Buffy and myself. My mum has been super attentive while it's all happening, so now we just need to get used to each other.