With a card that has a separate target, like the magician card does right now, destroying the card before it reaches the target would stop it from taking effect, and also (obviously) remove it from her deck until she can make a replacement. For cards that target her specifically, or that she's chosen to target her, like the Hanged Man, the effects take hold immediately, and destroying it wouldn't stop that.
Lisa
Lisa reached forward and whapped Ev lightly on the back of the head. "Ev, be nice, that's our teacher." Discipline out of the way, Lisa was content to wait for the teacher to tell them what to do. English was always one of her favorite subjects. She loved writing almost as much as she loved reading, and was currently working on writing a book.
Cynthia
"No..." Cynthia backed up a step. For a moment, she had been in Cedar town for a moment, but now she was somewhere else. Somewhere terrifyingly familiar.
Rain poured down around her, making the ground muddy and slick. Blood seeped from a wound on her head and one on her chest, mingling with the blood that coated her arms up to the elbow. The blood of twenty four of the fifty soldiers sent to take her life.
And at the rear of the group, overlooking everything, was someone she knew she would never see again.
Her father.
"No, no, no, nononononono! Go away! Go away, go away go away go away! You're dead! Gone, killed, you can't be here! Why!?" She lashed out, striking at the closest person she could see, a feral mix of fear and hatred taking over her actions.
Trisana
"You want to fight?" Trisana said, her voice carrying a bit of an accent, "We'll start this off with a bang, then." Pulling a deck of cards from her pocket, she closed her eyes and quickly drew two cards.
"Tarot Magic! Misfortune!" She yelled, revealing the cards.
Hanged Man (Reversed) - Normally would cut the caster's physical abilities in half. Reversed doubles the caster's physical abilities.
Magician (Reversed) - Normally would double the target's magic power, Reversed halves it.
"I can work with this." She said, tossing the Magician card at the demon who was fighting Nico. If it managed to hit, the target would be complete and the card would take effect. Otherwise the magic would simply fizzle out.
In the meantime, the Hanged Man card was taking effect. Normally negative, the reversed position turned it to her advantage. She grabbed one card from her deck, not activating it's effect this time, and charged it with magic. "Come at me, puppies." She struck one with a kick, and used the card as a knife to slash the next one. She would have no trouble handling these minor creatures, especially with her boosted strength.