My girlfriend is acting more rebellious than usual?

Usually she's pretty calm and isn't really into partying, but since we finished high school she's been going to nightclubs and really crazy parties. I don't really mind, but I'm a little worried because she's usually more soft-spoken. I asked her if she was okay but she just said it was because she was "from a sheltered family and just wanted to live for once in her life," which does make sense because her family was very over-protective. I'm just really worried about her, and it seems like she's taking this too far. She's been forgetting nights and has gotten thinner.