Undermining her by putting her in a vulnerable situation that's specifically related to her gender. Rape, threats of rape, loss of clothing, bondage with decidedly sexual overtones, etc. Overcoming sexual vulnerability doesn't magically make a character strong, either.

This entire thread is something I'm really struggling with at the minute. My novel is about two characters who share POV (ala game of thrones), one male, one female. The female is a young adult who's spent the past year in a labour camp. She has one friend, an old lady, her bunk mate. In the beginning of the story, she gets 'marked' by one of the camp guards. The entire story is about her struggling against this guy and trying to escape him. Furthermore, she only takes agency of herself towards the end when the male POV goes MIA and isn't there to protect her. She's a half starved, over worked, nineteen year old. It's just not feasible to have her able to fight against him. At the end she escapes with the help of male POV and takes out the evil guard herself using a gun.

I'm really worried I, as a girl myself, have created a really weak, pathetic female character.