Power struggles can be seen at many different levels between diffferent characters. One struggle occurs between Griet and the rather bratty child of Vermeer that constantly finds ways to undermine Griet's reputation in the household. She frames Griet for the "theft" of the hair clip, and ruins much of Griet's work. So, there is a struggle between those two characters. Then, Griet also has to struggle against Vermeer's rich patron who wants to have Griet for some rather unsavory purposes. She does not want to be taken advantage of by this man, and there is a definite power struggle that ensues. Griet also has a power struggle with Vermeer's wife when she becomes jealous of her. She demands that Griet leave, and Griet loses that power struggle in the end.
Then, take the character of Vermeer. He has to struggle against an emotionally volatile wife who is very needy and manipulative. He also has power struggles with his patrons, who demand certain paintings and even certain favors from him. He has to acquiesce, because it means his living for his growing family. His patrons like to feel powerful and in control, and they are the ones that hold the purse strings. Also, Vermeer and his mother-in-law have struggles, in a bit of a love/hate triangle with his wife.
Power struggles are a major part of the story, and add a lot of dynamic to the plotline. I hope that helped; good luck!