I wouldn't say Minfilia gets kidnapped all the time, but she never lifts a finger in a combat situation despite being armed to do so. One of the first things we do for her is go get her knife inlaid with materia as an intro to the system, and she carries it with her on her right hip at all times. Despite this, she... never once uses it, even when she has every reason to do so.

Maybe it's for cheese?

Anyway, on paper her job is to manage the Scions, and before Alphinaud comes into the story she's the diplomat. But Alphinaud supplants her in that role, and even as a manager she utterly fails given Thancred overworked himself to the point he became vulnerable and got possessed by Lahabrea. In the end Minfilia's really just there to give you orders and for fanservice (have you seen the size of her knockers and the butt cleavage window?), and with someone else giving you orders in 3.0 (Alphinaud) she really feels superfluous at this point.

Now, could they bring her back and reenergize her character? Absolutely. But when freakin' Tataru is being more proactive in improving herself, you really have to wonder...