Signing with Epic. Everything they did after HTNGU was messy. The last minute delay of Rock N Roll after it had been premiered already, the album delays, & the very minimal promo. When she did get promotion, it was always small-scale & she needed the Billboard Awards or VMAs to gain awareness for the album & for RNR.
I think the first one was changing her style, from brown to blonde hair while adapting a more "pop" sound, while the second came with not having a growth or development in her sound.
The 4-year break wasn't really her fault/mistake. The album suffered many delays because of her label. It was originally scheduled for release in 2009 but was ultimately shelved until 2011.
People were here for her then but she released a boring generic song, which showed no evolution. If she had released something a little bit better, I think her career would be in a very different place.
The Best Damn Thing is a great album but that change really hurted her career. + Taking 4 years break to release Goodbye Lullaby with singles that never represented it (exept for Wish You Were Here, and that one came late). Third one is signing to Epic which include other big mistakes like releasing HTNGU and then the RnR fiasco and taking other three months to release Let Me Go featuring one of the not most loved singers without a big promo. Hello Kitty too.
Releasing Girlfriend when her entire image prior to that song hinged on the whole 'anti preppy', 'anti bubblegum pop' music thing. She sold out and that's why I haven't seen it for ha since her second album.
The 4 year break. Don't know why she thought she could afford all that time off. The second is staying in the immature teenager image. That worked when she was a teenager but now she's a grown woman and people don't buy it anymore but she's so connected to it that people don't buy grown up avril either.