You don't need to feel bad about not liking a fictional character.
I wasn't fond of her at first either, in part because I couldn't understand her slang initially, but she really grew on me. I greatly respect her black/white view on good/evil and how people make excuses to justify doing bad things, which I feel is completely true. Ex: Every Loghain defender. It's in contrast to someone like Solas who sees good/evil in gray, and thus can "twist anything to fit anything" as Sera puts it.
I also found her views on elfyiness to be very refreshing; especially from an elven character. I've never liked the Dalish and their self-imposed segregation, whining about a past they never even experienced, blaming humans for it (which turns out to be bunk), etc. I feel Sera is dead-on there, and in her view to focus on the present. This applies to real-life people who follow tradition just because it's tradition, or feel some absurd kinship to dead people they never knew.
Sera's life has also been hard, including periods of being near-starving, and yet she doesn't play the victim and whine about it. She's very upbeat and doesn't try to make others feel bad for having it better ...unless they're a noble punching down.
She has her faults as well. She's very dismissive of the mage/templar conflict as them just causing trouble basically; pretty much having no sympathy for the mages because their rebellion is messing up her preferred world. That's just naive selfishness.
Also, her anti-elf views are so extreme that they discriminate against elves in the present. I'm with her on scorning those clinging to romanticized past-elf ideals, but criticizing people like Briala for working towards helping elves in the here and now is just stupid. Elves currently are treated poorly in large part just because they're elves. That shouldn't be ignored.
I can get why you wouldn't like her with what's presented; especially if you dislike the qualities about her I like. She also happens to be the only companion with a constant kick-out option, so maybe the developers suspected you'd feel this way (and intentionally didn't give such an option for Vivienne to vex us).