She's crazy, insane or has been put (often emotionally) 'off balance' by something. "Whacked out" here could be something mild, like "off-kilter" where a person feels slightly 'off'. Alternatively, it could have a stronger meaning, like "screwed up", "out-of-her-mind" etc. Remember, there's the expression,"out-of-whack", which means something, normally systematic, is suddenly not running smoothly or at all. So, "whacked out" is the result of a situation 'out-of-whack.' The word "whack" means, literally, to hit something. Compare.: If your coin gets stuck in the vending machine, give it a whack. vs. I was totally whacked out after my third espresso with all that caffeine. Oh, by the way, if someone says "yo, that's whack" that's (gansta) street slang for something unusual or just plain ridiculous: "She fly? No, she whack!"

whacked·-out adjective exhausted stoned (sense ) wacky, crazy, bizarre, etc.

she's crazy

It means exhausted, tired.