Princess Alice would happily kick the asses of her captors and take names afterwards, if she wasn't greatly outnumbered by her kidnappers, who are all heavily armed and have her imprisoned within an inescapable prison. Therefore, she figures it's better to wait for rescue rather than try to break herself out.
Princess Alice is one of many hostages, both male and female, but she is considered the most important one.
Princess Alice is wheelchair-bound, so she's disadvantaged against a physical attack.
Princess Alice lived a sheltered life, and doesn't have the skills to defend herself or escape without guards.
Princess Alice's agricultural studies, on work vital to the kingdom, absorb so much of her time that she couldn't train herself to a level of dealing with specifically trained kidnappers.
Princess Alice, a civilian not trained to fight, was trapped by an enemy attack and gave up her chance to escape to get some more children away from the enemy.
Princess Alice was blinded by a surprise attack and kidnapped; she hasn't been trained to work blind.
Inverted: Alice is the Action Girl who saves anyone in danger.
Zig Zagged: Alice gets herself into a situation where she needs to be rescued. She not only rescues herself, but also her rescuers. Then she pulls a Heroic Sacrifice so they can escape a bigger threat.
They don't kidnap her because they know she's an Action Girl.
Enforced: "The Big Bad needs to be established as such. He has to Kick the Dog in a way that will affect Bob on a personal level and give him a justification to chase after him. Let's have the Big Bad kidnap his girlfriend!"
Lampshaded: "I hope Bob arrives soon. I don't like being locked up in here."
Invoked: "We need a hostage worth good money. Princess Alice is in no position to defend herself; capture her."
Princess Alicia deliberately goes down to the crime-ridden docks to be captured, thus giving the king's men an excuse to break into the house of the high-ranking noble who is the head of the kidnappers' guild.
Princess Alys goes into bandit territory to haggle with the bandit chief, knowing he is treacherous — and that her capture will sort out The So-Called Coward and Miles Gloriosus among her suitors.
Defied: Princess Alice has been trained in self-defense, so she dispatches those sent to capture her.
Discussed: "You can't expect Princess Alice to save herself... she's badly outnumbered and she's had no weapons training."
Conversed: "By using the damsel in distress plot, the producers can appeal to their target audience; role players."
Princess Alice is kidnapped by the Big Bad, and put through Break the Cutie, in which the Big Bad tells her that his Evil Plan only works because of her helplessness. Bob saves Alice, but the trauma of being unable to do anything while Bob risked his life to save her has severely scarred her. She breaks up with him because she doesn't want to be The Load anymore.
Played For Laughs: Princess Alice getting kidnapped is an Excuse Plot to get the story going, and happens every week, like clockwork. Princess Alice is resigned to this, and greets each kidnapping with a sigh, whiling away her hours in the dungeons.
Played For Drama: Princess Alice being kidnapped is a devastating experience for her, Bob (her rescuer and lover), and the people of her kingdom. Each time it happens, Bob goes through much angst over allowing her to be taken again, and Princess Alice gets progressively more insecure in her own power each time she allows herself to be taken, which impedes her abilities as a ruler.