Well generally speaking if she was having self-esteem issues then the sudden self love of the 1st two's relationship, hime and gal, would be at odds with that. Not to mention how KumaKaren was surprisingly able to come out of her shell at all.
I'm also noticing we're getting the parts of Karen that she likes the least about herself in order of what she dislikes least. Like she's trying to present our male MC with the parts of herself she thinks are good as a shield and that going forward from this on we're going to see parts of herself that she either outright dislikes or are the core root of her self-loathing.