I suspect their decision was twofold:- to prevent exhumation at a later date.
To prevent anyone else knowing where she is - gawkers or even her own Mother.
Let's say that Cindy did cremate Caylee in spite of Casey's wishes... which I still don't believe because I believe if they went back on any of Casey's wishes, I believe that JB would have filed an injunction... Cindy will not admit to it on the stand during the penalty phase.
It's not that I don't think that Cindy is capable of doing something like this, because she is 100% capable of being this spiteful and, in a way, she had every right to be since Casey murdered Caylee, but I still don't see Casey allowing it to happen. There is no way that Casey would have conceded that easily. To allow Cindy to have Caylee all to herself? To have the last say? I just don't see it?
Either way, I don't believe this "event" in the Anthony saga will have any effect on whether Casey is given life of death.
Now, I will be the first person to admit that the Anthony's drive me bat-dung-crazy and I personally would never want to be in the same building with them, let alone live with them for any amount of time, but Casey had every opportunity to get her life together and make a decent life for just her and Caylee. If she really didn't want Cindy to have any control over Caylee, as Caylee's mother, she had the right to decide whether Cindy could see Caylee or not. There are many Grants in the State of Florida that help young, single mothers. Education. Reduced rent. Day care. It was right there at Casey's fingertips. She could have worked, went to school, and gotten her and Caylee their own little place if she wanted to. Young, single mothers do it all the time. Casey was just too lazy. SHE allowed Caylee to stay in that detrimental environment that was the Anthony home. It all comes down to Casey having choices. Choices that adults have to make. Choices adults with children have to make. She made the most selfish choice by deciding to take Caylee's life in order to escape the grip Cindy had on her. It was the wrong choice and one that she is going to pay dearly for.
Knowing what I know about the Anthony's, if I were Mallory and I was seriously considering marrying Lee and having a child, I would make sure that there are CLEAR LINES drawn about Cindy's involvement with that child.
ETA: I might even suggest Mallory get it in writing and notorized!