She can say that because it's her opinion, and she's as much allowed hers as you are yours. Neither are necessarily right. But to assume you're always right and come back with indignant phrases like "how can you say that?" without any real backup just shows how young and naive you are, and how far you have to go before you progress to more mature music.
And while we're at it: is there any way on God's green Earth that you can make, or take part in, a thread without making it about Slipknot? You started this asking what seemed a valid question, but quickly and very predictably at this point brought it back to your favourite topic. Can you go five minutes without mentioning the "S" word? Talk about musical tunnel vision! You really should see your doctor about that...
Wake up and realise there is more to the world of music than bloody Slipknot, and people are not all going to agree with your contention that they're the greatest band ever put on this planet. It's called having taste.