Normally I don't want to spoil to the surpirse, but I find honest the best policy to getting shit done when bold face lies taken at face value doesn't do the trick.

But Fran isn't actually going to summon Titanica, but an illusion of her, because Fran is well aware of the destructive potential of Titanica and hopes to use the bluff of total annihilation to make Helena go all out on the radioactive monster, which may or may not give Fran an opening to actually get to Helena or whatever the objective of this battle really is.