These Should Never Be Said To Her...
"What did you do to your hair?"
Unless we've cut our own hair—this is not common—someone else did something to our hair. It wasn't us. And most likely we've gone to a lot of trouble and expense for it. "I like your new haircut" is infinitely better, and shows you're paying attention. It's also far superior to the generic "You look different," which tells us you're as clueless as ever.
"They both look the same to me."