Okay here is my take on the big fight... Let me first state that my daughter had a child as a teenager so I know how a grand child can be used to manipulate for what the mother wants or doesn't want. Yes I could have taken her to court for custody of him the problem is you are required by law to first make the complaint to Childrens Services (so you fear they will just take the child until resolved), then you must locate the father because he gets first right to the child if successfully taken from the mother (once again you fear losing your grand child) and then you have to know the fathers parents are they also going to try to get custody if the mother should lose custody. All of this does not happen in a few days rather it takes from 12 - 18 months because of home studies and other evaluations that must be done, which when you are in the middle of this seems like an eternity. Then you need the financial ability to continue this effort which can be $10,000 - $15,000 (which I don't think the Anthony's had).
Anyway the fight...
I think there was a big confrontation with Casey by Cindy over all the stealing because she had stolen from both the grand parents (Cindy's mother and father) Cindy's mother is all over her to do something about this daughter that is out of control. Cindy hates this because her image as June Cleaver is shot to he!! and her mother probably told her in no uncertain terms she is enabling Casey. I think and Cindy has admitted Casey has stolen tons of money from her and George but it was ok until Cindy felt her image was tarnished by the stealing from the grand parents.
Cindy confronts Casey, there is a big fight, Cindy pulls the credits cards and the ATM and tells Casey that is it (tough love) and Casey must move out until she gets het act together Casey tries to use Caylee as the bargaining chip threatening Cindy and George they will never she her again if they do this, but Cindy is confident she has been to a counselor and probably was going to get an attorney to try to get custody of Caylee (in her mind she WAS going to get custody) because of Casey's lifestyle and Cindy knew Casey was drugging Caylee so she could party. Casey leaves and goes to TonE for comfort, booze and sex, she goes back the next morning and takes Caylee with her. That night June 16th she had no place for Caylee to sleep because she could not take her to TonE's to sleep and she had no credit cards so she was going to sleep in her car with Caylee and by tomorrow Cindy would be crawling back and give her whatever she wanted. Caylee though was not used to being away from her grand mother and was crying she wanted to go home to her grand mother, probably even a little (justified) tantrum, Casey became enraged with jealousy did not want to hear one more word from Caylee and wanted the comfort of her latest conquest TonE, Caylee was interferring with that desire, in a rage (like her father's) she killed Caylee. This was the pay back to Cindy for her betrayal, justified because Caylee did not love her she loved her grand mother and grand father, so Caylee betrayed her as well and needed to die for it. I do think either George or Cindy helped her dispose of the body (leaning towards George) because they blamed themselves for what Casey did.
They are covering for Casey because they feel guilty and they have already lost Caylee and they know they cannot change that so they do not want to lose Casey too.
Soory for the long post... just my opinion in short form. I could go into a longer form but I don't want to torture you all.