Hostel 2
(2007)

After her two friends are killed, Beth (Lauren German) turns the tables on Stuart, the man torturing her. She holds Stuart hostage until the man in charge of the whole operation speaks with her. Beth offers him as much money as it will take to save her (she is very rich), and the man accepts on one condition: she must kill someone to join the club. She agrees and proceeds to castrate Stuart, leaving him for dead. The final two scenes show Beth getting the bloodhound tattoo that signifies membership, and then beheading Axelle, the woman that led her and her friends to the ill-fated hostel.

PS. Spoiler for the start of the film: Paxton (Jay Hernandez), the lone survivor from the first film, is beheaded.

 Thanks Casey!