To me, what separates a good depiction of a female character from a bad one isn't her strength, but her agency. Loosely, agency means "freedom." Yes, it's a feminist term, but it's of tremendous use in measuring whether a female character is a strong one, or a sexist stereotype.
To measure a character's agency, ask yourself these questions:
- Does she make a decision?
- Is that decision important to the plot?
- Is her decision coerced, or between two awful outcomes?
- Does she deal with the consequences for her decision?
If the answer to 1, 2, or 4 is "no," or number 3 is "yes," I'm afraid you haven't a strong female character, but a flimsy cardboard replica of one. I don't care how much she can bench press; if she's there to be the hero's prize, to reinforce the hero's decision, or to be an obstacle on the hero's path to success, she isn't strong.
Lots and lots of books have female characters who don't have agency, and that's okay (depending on who you want as your audience, anyway). But if you think you have a strong female character and she doesn't pass the above test, you're fooling yourself.
There are also the problems of a man-with-breasts, who is a female character who doesn't act like a woman. That one's harder to articulate, because gender lines are frequently blurred. A female character can be cold, insensitive, or indifferent to children, and still be feminine. (A female character can also be kind, sensitive, or loving to her children, and still be strong.) What tends to put most characters into the definition is a combination of factors, most of which ignore the reality of growing up female in modern (or medieval) society. If she not only never had any limitations on her knowledge of fighting styles, but disparages other women who do, she might be a man-with-breasts character.
If you're in doubt about your realistic depiction of a female character, I'd recommend asking some female friends for input. Not just one, unless you know she won't lie to you, and she's pointed out bad female characterization to you in the past. Just as there's no such thing as one way to positively depict female characters, there is no one female perspective on what is a good depiction. So, ask around, get a good idea of what your heroine is missing, make sure she has agency, and you're on the right track.