Let's put the worst face on it. Say that Lisa is actually some incredibly vain person who has regular waves of delusion which cause her to go in for monthly and totally unnecessary lip injections. In this version of reality, she's got no relatives with big lips, no fairly obvious photos from early in her career which show she always had fairly sizable lips, no bad lipstick choices which make the problem seem even worse. She's just vain, delusional and setting a bad example for other wanna-be Soap stars out there watching.
This affects her dancing how?
Subjectively, I think it's obvious that Lisa has to be working harder than just about anyone. She's got another full time job. She's got a big family. No matter what, she's certainly vain enough to have to invest a lot of time preparing her physical appearance. And she's considerably older than Stacy and Drew, if not Jerry (who's about a year older than her).
And yet she's dancing like a 20 year old, albeit one with big lips. She improves week after week--which in a way makes her the most reliable contestant out there.
Her effort or talent or work ethic won't matter a bit if someone hates her lips, or her job, or her husband. Sometimes people pick emotionally, not logically. I'm at the point where I, at least, am realizing there's probably nothing to be done to change that.
The reverse is true too. Some people will vote for her only because she's a Soap star (just like some will only vote for Drew because they liked the music group he was in, or for Stacy because they like wrestling).
In other words, a huge portion of this has totally nothing to do with how they dance. It's sad, and inevitable, and true. The endless lip comments are just the darker side of it. Some people see the world in a way which is conducive to popularity contests, some use logic. Short of changing the thinking patterns of a good portion of humanity, there's little to be done for that.