In Season 3, because of her on-and-off feelings, she manipulates Ross' then-girlfriend Bonnie into shaving her head. She later kisses Ross, which re-ignites his feelings for her which ultimately leads him to break up with Bonnie on the same night
Rachel's lie about being engaged to Ross resulted in her father confronting Ross in front of his girlfriend, Mona, causing problems in their relationship.
In continuation of her will-they, won't-they romance with Ross, she shows up at his wedding with Emily to tell him she loves him.
In season 5, Rachel joins a literature class with Pheobe and then doesn't do the assigned homework. Instead of reading the book as needed, she cheats and presents Phoebe's insights as her own, getting her friend into trouble.
After the birth of her daughter Emma, a misunderstanding with a ring led Rachel to agree to marry Joey. She did not have romantic feelings for him and only recently had a baby with Ross. This decision caused complications and not only strained her relationship with Ross but also almost ended Joey and Ross' friendship.
In Season 6, she blatantly lies to her roommate Phoebe Buffay about where she got the new furniture. Phoebe hates Pottery Barn because its products are mass-produced and not unique.
Rachel kissed Ross on the night of Monica and Chandler's engagement celebration, revealed her pregnancy (albeit not on purpose) on the day of their wedding, and even took the name Monica had chosen for her future baby.