I wouldn't say that Zelda is an I-Win button against Rob, but she has some things.
Tips from my own experience:
Learn to use Nayru's Love well in this matchup. This requires you to predict, not react. When you see the light on Rob's head go red, that means his laser is full. That means your opponent is losing usable charge time every moment he hasn't fired off his laser. Random and out of place, but i love your avatar. Anyway, when that red light is on, weight for a moment when, if you were ROB, you would fire your laser. At that moment, press B. His laser will come out at the same time as NLove, and he'll get hit. After a while, ROB's will start trying to mix it up, but you will still be messing with their game. OK other random comment, who is the girl in your sig chewing on a mouse cord?
Similar psychology can be used for the gyro, but remember that at many ranges it won't get all the way back to ROB, so you might as well take the less risky option, shield/airdodge. If it hits the ground you can pick it up, but the gyro isn't that conducive to Zelda's moveset, usually. You consider just tossing it away so ROB can't have it. (ROB definitely can have fun with it)
Learn to spam L if you get hit by Rob's fair. Rob's fair combos into itself like crazy, and Zelda's aerials simply are too slow. Zelda's aerials are great for moments when a character is confused in the air, or did something to early or too late, basically her air game is a punish game. Don't go head to head with ROB in the air, but if he opens him self up (like, maybe a missed nair), then punish it with a lightning kick.
If you are new to the character, which is kind of what you seem to be saying, try to skim a guide or something. I think Spazn has one that's at least ok, somewhere in here.
Main point for player's new to Zelda to know is, Dtilt is more awesome than you know. Every day i play the character i use dtilt more. Oh, and bair is faster and better than fair. In general, SH Din's is better than standing Din's. More or less, that's good enough to know, then practice using the character.
Ooh, maybe another thing i should mention is that Zelda players tend to spotdodge, a lot. Why? I dunno. Her grab is definitely not the best in the game, but downsmash after spot dodge is a really good tactic on the other hand.