Victoria was 14 years old. (Sure, Deborah Watling was 19 or 20, but the character was 14.) Although she'd had a sheltered childhood, and was then orphaned by the Daleks before being kidnapped by the Doctor, she learned pretty quickly.
Her main specialty was pretending to be a naive, sheltered little girl so she could con the bad guys. That, and screaming loud enough to actually kill the monsters.
The Doctor and Jamie constantly tried to get her to wear shorter dresses, and then teased her about it when she did. And Jamie fell in love with her. Did everyone involved in the show forget they'd established that she was 14 years old? Then again, Jamie was apparently meant to be about 17 when the show was out, before it was retconned to make him the same age as Frazer Hines, and back then, 17-year-olds with 14-year-olds wasn't considered to be as obscene as today's age of kids freaking out over 15-year-olds being with 14-year-olds. Not that you're reading any of this, you're still staring at the picture, aren't you?
Fans tended to assume that she was the best and the most important companion simply because a lot of her material was deleted and nobody could see what it was like (lol, with that logic, Dodo would be best companion! Though to be fair, the closest thing to good Dodo material was all deleted, so maybe there's some truth here), creating a massive Victoria hype, especially among the older British fans, that never really went away. Fans have since began to learn from the recovered audio that all she did was scream monsters to death, which is sometimes a good thing (see The Ice Warriors).