Anna must know that she is average in every way (it's probably part of her appeal), so she adopts all these phrases to make herself appear hip and relevant. Except she uses only the safest, most mayonnaise slang, the kind that you'd see etched onto a reclaimed wood sign in a basic witch's Pinterest board.
Regarding why she chose that house, it occurred to me that perhaps it was for tax reasons? I'm an American, so forgive my ignorance, but could it be possible that they didn't buy in a nicer area because of property tax rates? Clearly £1 million is a lot to spend anywhere, but as an example, a nice house in the Bay Area would still command waaaaay higher taxes every year compared to an even nicer, more expensive house in a less desirable part of the country. Maybe the cost balances out for them in the long run.