Katherine of Aragon took the measure of Anne with one of her clear blue-eyes sweeps and I felt a pang of fear that she would prefer my sister to me. (2.31)
Mary is immediately jealous of Anne as soon as she sweeps into the royal court. Her jealousy will soon shift, though: she will worry about Anne attracting the attention of the king, not the queen.
On George's other side was Jane Parker, watching me intently, as if she were trying to discover the trick of being a desirable girl. (2.172)
Jane is a girl driven by jealousy and envy. The family often brushes her off, but she will end up being one of the family's biggest enemies.
"Why should Anne be the one who says how things are done?" I demanded. "Why d'you always listen to Anne?" (2.577)
Mary sounds like a petulant child early on, whining about her family listening to Anne. Why does Anne get all the cute dresses? Why does Anne get all the boys? Mary is Jan Brady, and Anne is Marcia. Anne Anne Anne.
"Yes, look at you!" She rounded on me with a sudden flare of her dark energy. "Married when you were still a child and now the king's mistress. Half as clever as me! Half as educated! But you are the center of the court and I am nothing. I have to be your lady in waiting. I cannot serve you, Mary. It's an insult to me." (5.180)
The jealousy between sisters goes both ways, although Anne's is rooted in her superior attitude. She thinks she deserves more than Mary just because she's that much more fabulous, and she hates it when she doesn't get it.
"He's courting me," she said. "Openly."
"Anne, he is my lover." (14.322-14.323)
We have to wonder why Anne seduces Henry. Does she like him? Doubtful. Does she do it for power? Likely. Or does she only do it to take what Mary has? What do you think?
"She's just jealous. She'd give a king's ransom to be on the bed with me in the afternoon, and I'd as soon put my head into a mantrap as on her lap." (26.44)
Jane becomes nosier and more and more gossipy as the novel progresses, but it's wrong to write off her behavior as mere jealousy. In fact, she is working on betraying the family and bringing about their downfall. That's taking things to a whole new level.
"We both played a part to please the king. […] But I never forgot how he spoke to me about Henry Percy, and he never forgot that I was a Boleyn, an upstart like him. He was jealous of me, and I was jealous of him." (28.24)
Anne may be giving herself too much credit here. We doubt her uncle is jealous of her at all. He doesn't want to be king; what he wants is to be the guy pulling the strings in the background—you know, the guy really in charge. Anne is more jealous of him than he is of her.
I speak of you but there is nothing I can tell her which would reconcile her to your marriage. If you had married a prince and been unhappy she would have stood your dearest fun. (43.6)
George does a good job of explaining Anne's behavior to Mary in this letter. Anne hates seeing her sister happy because she wishes she were happy herself. Since she can't have that, she'll just try to destroy Mary's happiness. If Anne can't have it, no one should. Right?
"Well enough then," [Anne] said. "As long as neither of them are with him then I am content." (44.68)
Anne had no problem betraying the queen and stealing the king, but she becomes intensely jealous of Jane Seymour and Madge Shelton when the tables are turned. Doesn't feel so good to be on the other side, does it?