This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Ginger Snaps
Brigitte killing Ginger at the end of the first movie. Even worse is Brigitte's reaction.
Throughout the first movie, Ginger and Brigitte's relationship continueusly falls apart. At the begining they where the best friends they could have and by the end Brigitte stabs her in the heart.
Here is one example of their arguments.
Brigitte: You want me? Then stop hurting everybody else and take me, take me!
Ginger: I don't want you! I don't even know you!
Ginger: We're almost not even related anymore.
Ginger: I said I'd die for you !
Brigitte: No, you said you'd die with me because you had nothing better to do.
The scene where Brigitte infects herself with the werewolf curse in an attempt to reason with Ginger to take the cure. This becomes even more heartbreaking after you've seen the sequel, knowing that Brigitte's final attempt to save Ginger was all in vain, and she ultimately doomed herself, as well.
Brigitte: You wrecked everything for me that isn't about you!(cuts both her and Ginger's palms, then holds her hand, mixing their blood and ultimately infecting herself) Now I am you.
As quirky and a bit of a Cloud Cuckoo Lander that she is, you can't help but feel bad for Pamela after she discovers Trina's body, which leads to this moment between her and Brigitte.
Pamela:You've done a terrible thing. But... my tiny babies... now, it's one thing if you leave, it's almost normal, but no one's gonna take you from me. First thing tomorrow, I'll let the house fill up with gas, and I'll light a match. Brigitte:What? Pamela: We'll start fresh. Just us girls. It'll be fun. Brigitte: ...What about Dad? Pamela: He'll just blame me. They all will... Brigitte: ...This isn't your fault, Mom. Pamela: (clearly on the verge of tears) ...Yes it is...
In the second film, there is possible fate that awaits Brigitte after Ghost's betrayal. Here's the idea; she is being kept in a dark basement and is likely going to be forced to kill whoever Ghost feeds her. And in this series it's commonly believed there is no going back from a transformation. And cronologically speaking this was the last film, so it might just be Brigitte's final fate.
This exchange in the sequel, when Brigitte and Ghost are spending the night at Ghost's grandmother's house.
Brigitte: My sister and and I shared a room. Ghost: A sleepover every night. Brigitte: Kind of. Ghost: Do you miss her? Brigitte: ...All the time.
In the prequel, Ginger finds the werewolf who bit her (who was just a little kid) crying at his mother's grave and hesitates to kill him, instead she talks to him (doubles as a Crowning Moment of Heartwarming) saying "I'm sure she misses you too". This is followed by the boy being captured and being forced to die at his fathers hands.
Also from the prequel, there is the legit fear Ginger has when she thinks she will end up killing Brigitte.