Good thought. Another potential reason is that she wants the trial to happen before the remains from FL can be positively identified. I could see Tammy thinking (assuming it is Heather) that the remains can't be used as evidence until they're identified. Of course they can't be used as evidence prior to the identification, but LE will just expedite the process to be ready for trial. Just another bad scheme of Tammy's in an attempt to "outsmart" the system like her fake pregnancy.
Whatever the case, I bet she will end up regretting this move to speed up the trial because it's really only going to put her in prison sooner.