So people are allowed to criticize her and she's supposed to be entirely okay with it 100% of the time, but she can't react in a way that maybe made her feel better? She's not even being aggressive. So what if it's "immature?" That's not a reason to be angry at her. So she's using her lyrics/pictures to explain how she's feeling--because that's not what her career is based on anyway?
Being faced with negative comments as an artist in the late 90s is different than it is now. She still has all those same people from back then criticizing her, but now she has the general population doing the same. She may be overwhelmed, especially with all the hard work she's put this year. She's human, after all.