Rebel without a cause? Middle child issues? Whatever she's got, she's got it bad. The way we see it, Gertrudis is one of the bravest characters and essential to the novel because she symbolizes a stark contrast to the other female characters.
The blooming of Gertrudis's fiery sexuality is sparked by Tita's quail in rose petal sauce. While the rest of the family has mixed reactions to this dish, Gertrudis gets hot and bothered.
How hot and bothered, you ask? 1) She needs a cold shower. 2) She burns the shower down and has to run out naked to stay alive. Just at that moment, Juan, a smoking rebel soldier, heads her way. He knows "[Gertrudis] desperately needed a man to quench the red-hot fire that was raging inside her" (3. 190). Later on we get the whole story in a letter from Gertrudis to Tita, sent from the brothel in which she's working:
[Juan] left because I had exhausted his strength, though he hadn't managed to quench the fire inside me. (7.429)
Not only does she leave the ranch long-term, when she comes back she's a general in the revolutionary army:
The commission had been earned by sheer hard work, she had fought like mad on the field of battle. (9.592)
This is a pretty big deal, considering the fact that women in Mexico couldn't even vote until 1947. And while there were female soldiers at the time, there weren't many generals.
So, she fights, she drinks, she dances and she has sex. Yeah, we'd say she's pretty righteous. Personally, we would have liked to see her lead some battles, but we guess you can't always have the whole enchilada…