IMO, the one thing that marks a terrorist is the willingness to disrupt public life with violence. Only if Kira had said that she bombed a market place might I call her a terrorist. The institutions and residences of the occupying powers are otherwise fair game for a member of a resistance movement.
From "Defiant":
KIRA: You're really not cut out for this, are you? Being a terrorist, I mean. You're not very good at it.
RIKER: Really?
KIRA: You're acting more like a Starfleet officer who's more interested in intelligence reports and Cardassian politics than in actually hurting Cardassians. You have one of the most powerful ships in this quadrant under your command. Why aren't you out attacking every Cardassian outpost along the border?
RIKER: Because these stakes here are far greater than border outposts.
KIRA: Not for the Maquis, they're not, because
the Maquis are terrorists and the only thing terrorists care about is attacking the enemy. I know. I was a terrorist. And if I'd had this ship then, I would've destroyed Deep Space Nine. I would've hit the Cardassians so hard they would have screamed for peace, but I certainly wouldn't have gone flying off into the middle of Cardassia on some wild goose chase.
RIKER: I guess we're different kinds of terrorists.
KIRA: No, you're trying to be a hero. Terrorists don't get to be heroes.
T'Girl was kinda trolling, obviously, but in fact she wasn't entirely wrong. Kira is a self-admitted "terrorist" whose past and cause are sympathetically portrayed on DS9, an installation she admits she would have blown up in her role as a terrorist given a chance. DS9 did in fact have something interesting to say about terrorism and didn't shy away from complexity, or retreat into incoherent banalities artificially demarcating "resistance fighters" from supposedly demonic "terrorists." This was actually one of the show's major virtues.