#1 She is metaphorically comparing herself to a pitbull terrier, dogs bred for dogfighting and notorious for their trait of holding onto whatever they bite. She is suggesting she never lets go once she gets a hold on something.
#2 To crown something means to acknowledge it to have reached the highest or perfect state.
rollercoaster week - a week in which events went from high to low to high points.
To crown a rollercoaster week = the week's final event is a high point.
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