Assassin mode isn't a power, it's training. She always has access to it.
Anyways, Assassin/Batman Mara refers to the gal who can keep up with Caedus for far longer then someone of her power level typically could.
If someone said 'Mara vs. Caedus' in a thread, the answer wouldn't typically be 'Caedus in a close match.' But a close match is what it was.
That's why it's called Batmanning. There's no earthly way Batman can keep up with Superman. But...Batman tends to win almost every fight.
It's a fighting mode, and one that she doesn't just enter at will. That's why in the majority of her fights, she doesn't become enter assassin mode.
A close match indeed, with circumstances that were against Jacen.
"Batmanning" implies use of gadgets and other utilities on a frequent basis, which isn't exactly how Mara works. She's hardly an orthodox fighter, but she's no Batman, as I said.