Romilda Vane wasn't sure of herself in that precise moment.
She was crying. In her 6 years of Hogwarts, she had loved this castle, her second home, and this was unhinging.
"Crucio!" she was horrified by this shout.
A giant swept into the courtyard, and sweeping a giant scimitar across the field, knocked about twenty off their feet.
The transfiguration courtyard had become a place of violence, just like the rest of the castle.
Then, a second later, she recollected herself, and she thought
I am a Gryffindor! I am daring, I have nerve, and I am chivalrous! I am a Gryffindor!
And she cast the greatest variety of transfiguration spells she had ever seen.
She summoned the last of her skill, and silently, powerfully, Romilda Vane realized herself, and she let out a stream of spells.
The Death Eaters didn't know what hit them.
And she found her other friends, and even more. They were back to back, in a circle, and the friends she sat with in the lavatory, gossiping about what couple was having a row, suddenly became much more to her;
They were friends for life.
There are some things that you do with someone and can't help but end up liking them.
And knocking down a twenty foot giant off a bridge was one of them.
As the dementors swarmed, her friend fell with scream that lasted no more than a second. Another instant, and her friend was soulless.
She cast her first corporeal patronus, amidst the chaos, and the bright white, misty wolf sprang forth and brought what must have been a hundred dementors away from the area.
Her friend breathed a giant sigh of life, and they regained sense of where they were. They would keep on fighting.
She knew it.