can someone name this horror movie?

i remember watching this horror film years and years ago, and i can't rememeber its name.
basically all i can rememember is that there were two teenage sisters and one of them turned into some kind of monster by the end of the movie (i think it was a werewolf or something...)

i think this movie was made in the 90s.

also at the end, the sister had to drink some blood and she was sick, and then she chased after this monster around the house, and tried to get it to turn back into human form. but in the end she had to kill it, cause it was trying to kill her.

if you know what this movie is called, i'd really appreciate it, cause i wanna watch it again.
:)