Would it be a good idea for your Mum to come down for a few days to help settle her in? It would ease your Mum's mind and also give her a point of reference so that she can continue to build a relationship with your sister. At the very least, I'd try forwarding her an image of your street, details of the school, anything else that's on the web and would put her mind at rest. I know when I left home young it gave my Mum great comfort when I gave her information about where I was living and what went on in the area.