Someone on another board said that just because she's signed on to do the pilot, doesn't mean that it will make it on the air. There are alot of pilots that aren't accepted by the networks, and even if this one is they've been known to recast certain roles. This is a bad example, but if you watch the pilot episode of 'Roseanne' I believe there is a different actor playing Dan and Roseanne's son DJ. He was replaced by Michael Fishman later.
I think Beth was a recurring character during seasons 1 and 2, but this season Rachel Boston was added as a regular, probably since Beth had JJ's baby.
The actor who plays Uncle Pete, for example, is listed as a guest star, although he might as well be a regular because he's on quite frequently.