Probably some single choices like I Do Not Hook Up, All I Ever Wanted, Dark Side... But overall I think she didn't do any mistakes.

Hilary Duff took 7 years off

Releasing Power & Control as a single.
Taking so goddamn long to release Tropico.

The Harry fiasco.

No releasing Cuz I Can, Bad Influence and **** Like You.

Not giving Commander a full release in the US

Releasing what she wants instead of what label wants at GL era.

I would say working with Luke, but I wouldn't have a clue who Ke$ha was if she never met him.

I think her debuting with TiK ToK permanently made her look trashy to the GP, and none of the singles from the Animal Era (although Take It Off/YLIMD were not that 'trashy' video-wise) helped. After that, she probably couldn't even go a classy route without the GP thinking she's trying too hard to look "clean".

Personally, I think Take It Off could've done as well as TiK ToK if that was the lead single, and she could've not had the trashy party girl image. Then again, Take It Off is my favorite single of hers, so I'm probably a bit deluded.