I agree with ya, Cecybeans, that Casey likely got the first "notion" of getting the house from Cindy if it is to be believed about the CA/GA divorce and putting the house in Casey's name. Shady behavior breeds shady behavior, does it not? That is not a good thought to put in lazy Casey's skull.
So, SPECULATION, when GA and CA get back together and here's Casey preggers with Caylee, and then has the child out of wedlock, the 'rents are starting to complain and criticize Casey's stealing, work history, and child raising, friction begins to occur. The idea may have been planted in Casey's mind at various times about her "getting the house". In fact, by June 2008 she is NOT getting the house, she's close to getting the BOOT from the home (but they want Caylee to stay).
I think Casey was ANGRY at the alleged threat from the A's about taking Caylee away from her. I think she was ANGRY about them riding her @ss about the No Clothes Party when she told them she went to work and then Cindy went on her MySpace and then showed Casey she saw the photos and said, "You were AT WORK, HUH"? I think she was ANGRY at being usurped as the "mother" of Caylee. I think she was ANGRY about not being able to go to Puerto Rico. I think she was ANGRY at being called out on her stealing and was jealous about the attention Caylee got from Cindy, George and even Lee. I think the Father's Day event and not being invited or told not to come really set her off! I think she was ANGRY that they would even CONSIDER kicking her out (I don't think they would have anyway).