As part of the 1980's reboot, Nancy Drew learned karate. This was hailed as a good, feminist move. She can fight for herself! She's no longer a damsel in distress who gets rescued when the culprit shows up! (The 2002 Scooby Doo movie did the exact same thing with Daphne's character.)
Although they had good intentions in making Nancy Drew more of a modern feminist, I think there were three problems with making her a karate expert.
1. Her karate skills are plot-related. She can only use karate to win a fight, if the plot demands it. If the plot demands that the culprit gets away at this point, then either she fights badly, or she forgets about her karate skills completely. So the karate ends up being more of a curse than a blessing, because the majority of the time, she either fails at it, or she's an idiot who forgot she can disarm anyone bare-handed. Keep in mind, knowing karate doesn't stop her from regularly being captured and thrown into death traps.
2. This was hailed as a new, groundbreaking move...but it wasn't. The Hardy Boys had been fighting culprits for decades, before Nancy. She wasn't so much breaking ground as retreading old ground. The authors seemed content to have their only feminist development be "Nancy Drew acts more like her male counterparts", instead of "Nancy Drew moves so far forward, she bypasses her male counterparts".
To be fair, "Nancy fights culprits by herself" would have been an equalizing move in the 1960's. But we're talking about the 1980's Nancy Drew reboot. Well, guess what? The Hardy Boys got a reboot in the 1980's, too! In their reboot, they transitioned from dangerous fistfights to dangerous gunfights. So she caught up to them, just in time for them to move on to something else, meaning she still remained two steps behind them. Although, really, they still did a LOT of fistfighting, so she wasn't THAT far behind them...
3. There was no introduction. It just popped up at the end of Nancy Drew Files 2 without any warning whatsoever. On one page, she's normal Nancy, and on the next page, she's a black belt in karate who just beat up some culprits. That came completely out of left field, so much so that it was ridiculous. They should have mentioned her karate skills at some point BEFORE she used them for the first time, because it comes across as a cheap gimmick / deus ex machina scene.
Of course, this isn't a problem anymore, because now I'm in the 30's of that series, and it's firmly established that she knows karate. Still, I imagine some readers get shocked when they see her use karate for the first time, without any warning.