I've never understood that either. Resentful of being a stepmom perhaps, but I don't know what she would have been jealous of. Landen was married to someone else, TS was married to a decent man, she lived in a nice home, had nice vehicles, did not seem to be lacking for any material things. But we don't know what went on behind closed doors. JMO.
I think part of the anger towards her stemmed from the fact that TS claimed that LH and her uncle were harassing her and got her fired from a job by calling the place and telling them negative things about her and not to hire her. And the uncle of LH was supposedly the superintendent of the schools or something.