Less Than Perfect appeared to be poised to be her big breakthrough as an actress. Granted, it did have a reasonably respectable run with four seasons and about 81 episodes. But since that time, she has essentially spent her career (https://www.imdb.com/title/tt0320052/mediaviewer/rm4112168960/) as a supporting player instead of the lead.

I know that she's currently a semi-regular on the sitcom B-Positive, playing Thomas Middleditch's ex-wife but it seems like she's completely wasting her talent there. She also had a recurring role on American Housewife as one of the nasty rich women. And she was a cast member on Reba McEntire's short-lived ABC sitcom Malibu Country.

On theory that I read was that Sara's speech impediment probably held her back from getting more chances at being a leading lady. I don't really believe that because that didn't stop Drew Barrymore from having a successful career.

Another argument that I heard, is that when Sara started loosing weight, that essentially her of what made her stand-out. On Less Than Perfect and even before that, Sara was great as the quirky, chubby girl. But she's just kind of forgettable as the skinny leading lady.