Zelda asked Link to open the Door of Time and he agreed. She didn't physically force him to do it. Zelda didn't know that Ganondorf would be at the Temple of Time at the exact moment Link was there. Everything that happened was one giant coincidence. Besides, Link and Zelda were very young. I think they were both fairly naïve about the matter; Zelda for concocting a plan to save the Triforce, and Link for actually going along with it. Yet in the end, Zelda made up for her mistake by sending Link back in time 7 years so he could live-out his childhood.
Zelda evades Ganondorf for seven years while Link is trapped in the Sacred Realm by disguising herself as Sheik. In the manga it even suggests she worked under Ganondorf to keep an eye on him. You'd have to have guts to pull crap like that.
When Link awakens from his sleep, Zelda is the second to greet him and tell him the specifics of his quest. She risks her own life by saving Princess Ruto from the ice when Zora's Domain freezes, she takes a hit from Bongo Bongo which sends her flying, and she leads Link out of the collapsing tower of Ganon's Castle. She, with the help of the other Sages, seal Ganon in the Evil Realm and help return peace to Hyrule.
In OoT, Zelda is only captured at the very end of the game, because she reveals her identity to Link. During the rest of the adventure she is there to guide him and offer words of wisdom.
Zelda is also a stable character in SSB Melee, having the ability to fight as either Zelda or Sheik. In her original form she boasts strong magical attacks, and as Sheik she has very smooth physical attacks. Melee proves Zelda can hold her own.
1) A Gossip Stone says that Princess Zelda is a tomboy, which would explain why she chose to make Sheik a man.
2) Impa is the last of her race and would be the only one who could teach Zelda the ways of the Sheikah.
3) Zelda tells Link straight out that she was Sheik. "I apologize for meeting you in disguise, but it was necessary to hide from the King of Evil. Please forgive me."
4)
In SSB Melee, you choose Zelda at the start of the fight, then have the option of changing into Sheik by pressing down + B to transform.
5) In the official Ocarina of Time manga, Link discovers Sheik is Zelda before she can reveal herself to him.
6) And, finally... Not many guys would wear a suit that tight.
1) "This mighty weapon became known as the blade of evil's bane, or the Master Sword. It was so powerful that only one who was pure of heart and strong of body could wield it" (excerpt from A Link to the Past). I'm guessing that the only person in Hyrule who fits that description is Link, the Hero of Time.
2) It's too heavy. Maybe she can't pick it up, or she's afraid that if she throws it, it will fall off the cliff and into the abyss. Then where would Link and Zelda be?
3) If she throws it to Link, but he doesn't reach it in time, Ganon could knock it off the tower.
4) It's a way for the game designers to add more tasks/annoyances to the final battle. It allows for a change of pace; when Link re-enters the circle, Ganon moves more quickly. It also puts emphasis on the importance of the Master Sword, because that is the only weapon you can use to deliver the final blow to Ganon.
I'm placing my bets on #4.