Off the top of my brain pan:

When a legendary retired hit woman helps her timid granddaughter fight back against bullies, the teenager turns into a hit woman in her own right.

Notes:

Modest Blaise: I suggest you don’t use her. Not in your logline, no in your story. Because:

1] Don’t assume everyone immediately knows who you’re talking about. (I didn’t; I had to google.)

2 ] IMMEDIATE is a critical operative word in loglines. You’ve only go a few words, a few seconds to make one impression, the right impression. Don’t confuse, don’t puzzle, don’t give the wrong impression.

3] The character is copyrighted. Which means you have to get clearance to use her in the movie. Which — IF you can get it — is going to cost $$$,$$$ — yeah, six figures at least if it’s a major motion picture. By including that implied cost in your logline, you’re giving producers and directors a reason, an excuse, NOT make a movie from your script. Don’t give them that excuse

Teenager: just a thought. Think of the prime demographic for a ‘chic action flick’. (See Katniss Everdeen in “The Hunger Games”. Need I say more?) If you movie is a hit then you’ve hit the mother load of movie making: FRANCHISE!

In loglines, concept is more important than character. I think “a retired hit woman who mentors her granddaughter to become a hit woman” is a cool concept — a potentially viable hook. As in franchise.

One person’s opinion.