Amelia too had sensed the cold in the stairwell, but she had been more cautious about casting her patronus. She knew the others would be quick to cast, but she wanted to see what she was up against before she immediately went for her wand. From experience, she knew these types of things often played on people's most instinctual reactions, such as assuming a dementor with a sudden drop in temperature. It could easily have been a cooling charm placed there as a trick for incoming adventurers.
As they ascended the stairs, however, Amelia saw that it was indeed a dementor which stood before them, its sucking breath rattling. She could feel herself giving in to despair, her memories clouded with every time her parents had berated her for not getting a spell on the first try, making a mistake in a violin concerto, not being good enough to make up for her brother's shortcomings. The cold seemed to grow from the inside out, instead of the way it naturally worked from the outside in.
She could sense that the darkness in her mind was going to overtake her if she did not act quickly, so from some deep, barricaded part of her mind she pulled a memory that had been formed recently. A memory of a night where she had somehow lost the shy, introverted girl that usually dominated her life and instead had been a confident, outgoing girl who had danced a waltz and a samba with a boy whose smile had made her feel like the only girl in the room.
Expecto Patronum! Amelia shouted, louder than necessary for the spell to work, but as loud as was necessary to ward off any negative memories which might prevent her for correctly casting the spell. From the end of her wand, a transparent and silvery hawk glided above the dementor, already being repelled by Christabelle's tiger and the other man's wolf. As her patronus realized the attack had already been fortified, it swirled twice about the dementors head before turning to land on her shoulder, protecting her instead from any further emotional damage the creature might like to inflict.
Breathe... breathe...