Sentence:  [S]he has no fair pretence of family or blood. She was nobody when he married her, barely the daughter of a gentleman; but ever since her being turned into a Churchill she has out-Churchill'd them all in high and mighty claims: but in herself, I assure you, she is an <WSD>upstart</WSD>.” 
Meaning of the word marked with <WSD> tags:  One who has suddenly gained wealth, power, or other prominence, but either has not received social acceptance or has become arrogant or presumptuous.