Since there is no proof that we are aware of that proves ICA actually made or purchased chloroform - but the roll of tape came from the house and had 4 or more pieces cut from said roll - that's where I have no trouble finding premeditation. Aside from the possibility that if the chloroform was used and the COD - it could have been accidental.
Just like suffocation by any other means - there are several minutes there to change your mind - obviously she didn't.
However, we do have the tape and the autopsy says it was put on before decomp started.
I think the biggest thing in this case is the 31 days. The lying about why she waited to protect her family from harm - yet the kidnappers were perfectly okay with her doing her thing with Tony and having her cell phone and going out at night and going back and forth to the house, etc. I really don't think you need much else, but just in case, they do have the tapes with the lying, the June 20th picture and the endless array of other evidence.