She doesn't actually think that, you know. She has no concept of what that actually is. I'm willing to bet she heard it in a song, or on TV.
Unless it seems like she's having problems, I think this really isn't a big deal. Sure, she should know that it's not something she should be saying. However, her saying this, does not mean something is going on!! She probably repeated it once and got a reaction. So, that's why she's saying it again.
I wouldn't feel weirded out, because she doesn't KNOW what she's saying is inappropriate. She doesn't even know what sexy is.