Cheese (87.5%)
Oh, that’s where she left her lunch. She tossed the small wedge of cheese into her mouth and got to work.
Plank (12.5%)
Careful not to alert the guards, she set up one of the larger planks to act like a catapult and launched both herself and the diamond passed the two watch ponies.
“And then after that they just up and arrested her.” The Unicorn said.
“Woah, really?” The Earth pony replied, enraptured.
Twilight didn’t stick around to hear the rest of their conversation. Instead she quietly exited the building.
One last guard stood between her and success. A Pegasus stallion chewing some gum at the bottom of a short flight of steps. And he was armed.
Snap Neck
Diamond
Rifle
Jump
Liked the actually semi-logical reason for having the cheese - i.e. it was her intended lunch and just finishing it before getting to the plank.
I'm definitely voting for the Diamond (albeit with Twilight using her magic to slow the diamond's descent JUST enough where the impact will knock the guard out, but not kill him/her. After all, Twilight KNOWS that the police would look A LOT harder for a murderer than for a thief.
And, after that, two possible scenes both for set-up concerning Infiltrating the Airship.
The first scene has a pair of shadowy figures complaining about how somebody they didn't recognize stole the diamond before THEY could (these would be agents of the Toppat Clan Expy).
The other scene involves Twilight getting hit with a tranquilizer dart while trying to find a fence for the stolen diamond and gets taken away by a pair of Pegasi in uniforms for the Expies of the Government while she is still sleeping, one of the Pegasi commenting that the Captain is going to be extremely pleased they were able to capture Twilight with such little difficulty and without anybody getting hurt.
A possible starting dialogue for the "Infiltrating the Airship" portion:
Whoever you cast as the Captain: Ah, so you're awake. Splendid. I was worried that my troops put too much tranquilizer in that dart.
Twilight: Where am I?
Whoever you cast as the Captain: We really do want to give you a chance to work toward redemption. We DO have you on criminal charges. Attempted bank robbery, well, that trial fraud was your lawyer's idea, so we can't put THAT ONE on you, but you were still acquitted through fraud and stealing a multi-million bit diamond. However, a pony with your abilities would be too much of a waste rotting away in prison, so we want to give you a chance to do an extremely dangerous mission in exchange for earning a full pardon as well as a rather respectable paycheck.
11293009
Hey! No backseat authoring.
11293058
Okay. Sorry about that. (sheepish grin) Just let my imagination run away with me. Again, I profusely apologize.
11293067
It's alright. No hard feelings.